Lenslet array systems and methods

ABSTRACT

A stacked array magnifier (SAM) forms a magnified, demagnified or unit image of an object. The SAM includes one or more non-refractive lenslet arrays and one or more refractive lenslet arrays to form a plurality of lenslet channels. Each lenslet channel has at least one refractive lenslet and at least one non-refractive lenslet. SAMs are combined and tiled to form a scaleable display of flat panel displays. Multiple SAMs are used to increase magnification selectively. Hybrid lenslet arrays of the invention are also useable for optical processing and non-imaging applications.

RELATED APPLICATIONS

This application is a continuation-in-part of commonly-owned and U.S.application Ser. No. 08/786,752, now U.S. Pat. No. 5,973,844, entitledLenslet Array Systems and Methods and filed on Jan. 24, 1997, which is acontinuing application of U.S. Provisional Application No. 60/010,670entitled Stacked Array Imaging System and filed On Jan. 26, 1996, eachof which are hereby incorporated by reference.

BACKGROUND

Imagery is presented in many forms. In the classical optical camera, forexample, light energy from an object scene is focused through glassoptics onto a film formatted image plane where light sensitive filmrecords the scene. Typically, the film format corresponds to "35 mm"film, which translates to maximum linear dimensions of 36.3 mm(horizontal) by 24.2 mm (vertical), or a vertical-to-horizontal ratio of3:2.

In the electronic age, the classical film-formatted camera is beingquickly replaced by the solid-state camera utilizing charge coupleddevices such as the "CCD" array. Typically, the CCD array is formattedto conveniently correlate with the computer display screen, which has ahorizontal-to-vertical aspect ratio of 4:3. In this manner, the CCDarray and computer display are matched on a pixel-to-pixel basis.

However, regardless of the high quality image presented by the classicalfilm-formatted camera, its optics and housing are unsuitable forapplication with the CCD array. Accordingly, as users convert to digitalcameras, their older film-formatted cameras shall become obsolete. Notonly will the typical user have to buy a new camera, i.e., the digitalcamera, she will discard or retire the film-formatted camera, creatingboth cost and waste.

It is, accordingly, one object of the invention to provide apparatus andmethods for adapting film-formatted cameras to solid state devices suchas the CCD array in a compact and useful manner. A corollary object ofthe invention is to provide reimaging methods to achieve selectedmagnification and/or demagnification for each of the tangential andsagittal axes.

The prior art is known to have created optical systems for relaying andmagnifying or demagnifying optical images by way of an optical systemsuch as a relay lens. Specifically, in the prior art, it is known that arelay lens can be used to relay one image plane to another image planeat a selected magnification (or demagnification) ratio. However, such anarrangement is unwieldy and would generally double the size of theclassical camera, making the approach nonpractical as a solution to theabove-described problem. Further, it is very difficult, and thus costly,to simultaneously provide selected magnifications for both of thetangential and sagittal axes. By way of example, it is known that anastigmatic optical element provides such a bifurcated magnification;however, this element requires additional aspheric processing, addingcost, time and complexity to the manufacturing process.

The problems discussed above are symptomatic of a wide range of displayproblems and inconveniences experienced today. In the electronic andmedical world, for example, imagery is often displayed on a television(TV), a computer display, the liquid crystal display (LCD), the cathoderay tube (CRT), light-emitting diode arrays, and back projectionsystems. It is often desirable, however, to illustrate the electronicdisplay in a different format such as to a wider audience on a largeformat display. In the prior art, for example, complex projectionsystems are sometimes used to relay a smaller electronic display onto alarge, reflective surface such as a white wall or a projection screen.However, it is widely understood that projection display systems arelarge in size, expensive, and heavy; and they inefficiently consumelarge amounts of electrical power. They are also generally limited touse in darkened areas due to low luminance output and poor efficiency.

An electronic display that is generally defined as a Flat Panel Display(FPD) has other difficulties that are not adequately addressed in theprior art, such as limitations in luminance and angular view. The activematrix thin film transistor liquid crystal display (AM-TFT LCD), thepassive LCD, the field emission display (FED), and other FPDs (such asplasma displays and electroluminescent displays) each havecharacteristic angular fields due to inherent construction, polarizingfilters and fore- and back-light characteristics (if required). Oneexample of the angular limitations inherent in a FPD is readily seen inobserving a portable computer screen from different angles: the portableFPD is barely visible, if at all, from viewing angles greater than aboutforty-five degrees from the normal to the screen surface.

The angular and luminance limitations associated with viewing a FPD arethus significant. Most observers prefer to view an image that is highlyuniform in luminance over a wide field angle. This further compounds thedifficulty in converting the FPD to a large format display. In addition,daylight viewing and the suppression of glare often necessitateadditional screens or intermediate optics between the FPD and theobserver, adding other costs and complexity. In certain applications,the prior art has attempted, without great success or efficiency, toimprove the field of view of the FPD through the addition of diffractivespatial filters placed adjacent to the FPD screen.

There is the need, therefore, of enhancing the performance of the FPD.It is, accordingly, an object of the invention to provide apparatus andmethods for enhancing the luminance and field of view of the FPD. Afurther object of the invention is to provide systems for converting theFPD to a large format display with improved luminance and field of view.

Highly commercial electronic displays have still other difficulties. Forexample, very large commercial advertising and stadium-sized matrixdisplays are assembled using tiles of bulbs, CRTs, light emitting diodes(LEDs), or LCD panels. Not only are these systems limited in resolution,color (note, e.g., that LEDs are typically one color) and generaloptical performance, they are expensive, costing in the neighborhood of$100,000 per square meter. They additionally have low reliabilitystandards and few specifications or limitations on weight, powerconsumption and efficiency.

It is, accordingly, an object of the invention to provide a system whichtransforms the image presented by an electronic display--such as theLCD, the CRT, the FPD, phosphor displays, an array of LEDs, a computerscreen, and a pixelated object--into a reformatted image with enhancedor modified features, such as with selected magnification, astigmatism,distortion, optical correction, optical processing, and Fourier content.

Another object of the invention is to provide apparatus and methods formagnifying or demagnifying an image of an object with a compact andsubstantially monolithic optical system.

Still another object of the invention is to provide methods ofmanufacturing and constructing combinations of lenslet arrays to achievemagnification or demagnification selectively.

Yet another object of the invention is to provide optical correlatingapparatus and methods for conveniently achieving Fourier processing ofan electromagnetic field.

These and other objects will become apparent in the description whichfollows.

SUMMARY OF THE INVENTION

As used herein, "magnification" is sometimes used to denote bothmagnification and demagnification. Accordingly, "magnification" issometimes used herein to denote a magnification of greater than one, ademagnification of less than one, and unit magnification.

As used herein, a "lenslet array" refers to an array of microlensletsthat are arranged into an optical substrate surface. A single lensletarray can therefore include an array of refractive lenslets or an arrayof non-refractive lenslets. As used herein, "non-refractive lenslets"generally mean diffractive lenslets. However, non-refractive lensletscan include holographic steering lenslets, phase modulating lenslets,and index modulating lenslets (including gradient index modulationformed through ion implantation and ion exchange, and effective indexmodulation using nanometer cuts within a substrate surface). A lensletarray is formed with an optical surface substrate which is typicallyplanar except for the micro-features of the microlenslets. However,those skilled in the art will appreciate that lenslets arrays can beformed internally to an optical substrate--and thus not on thesurface--or onto curved surfaces (e.g., macrolenses) which provideadditional optical power.

A "stack" as used herein refers to a plurality of lenslet arraysarranged substantially adjacent to one another to operate as a singleoptical system. Generally, a stack has at least two lenslet arraysforming an array of "lenslet. channels," each of which has at least onerefractive lenslet and at least one non-refractive lenslet. In order toachieve radiation transfer along each lenslet channel, each lensletarray in a stack typically has like numbers of lenslets so that there isa one-to-one correspondence between the lenslets of one channel (thatis, each lenslet of each array has a corresponding lenslet in each ofthe other arrays; the corresponding lenslets forming the channel betweenthe several arrays).

As used herein, a "tile" refers to mosaic of like elements to operate,substantially, as a single element. In the typical case, a tile can beformed, for example, by an array of like lenslet array stacks which areabutted, end to end, so as to substantially function as a single stack.

As used herein, a "stacked array imaging system", or "SAM," refers to animaging system such as a stack arranged to view and image objects. Forexample, a SAM can include a magnifying or demagnifying optical system.

As used herein, "pixelated" refers to the quantized nature of certainobjects and images. For example, most computer displays are made up of athousands of pixels emitting light energy at the command of thecomputer's central processing unit (CPU). Such a display is "pixelated"since it is quantized. By way of another example, a solid state devicesuch as a CAMCORDER records continuous, real-world imagery via a CCDarray; and the data captured by the CAMCORDER is thus pixelated or"discrete." High speed computing via fiber-optics and electrical pathscan also be "pixelated" in that data, often made up of large digitalwords, are processed in a massively parallel fashion (sometimes denotedherein as "massive parallel processing" or "MPP"). By way of comparison,real world objects like a human being are continuous; and a picture(i.e., an image) taken of real world objects onto film emulsion is alsocontinuous since it is not quantized.

In one aspect, the invention provides a stacked array magnifier (SAM)for forming a magnified image of an object. The SAM includes one or morenon-refractive lenslet arrays and one or more refractive lenslet arraysto form a plurality of lenslet channels. Each lenslet channel has atleast one refractive lenslet and at least one non-refractive lenslet,and the lenslet channels between at least two adjacent arrays are slopedrelative to an optical axis between the object and the image. The slopedlenslet channels that are further from the optical axis have largerslopes than the sloped lenslet channels closer to the optical axis.Together, the slopes of the several channels provide selectivemagnification between the object and the image.

In another aspect, the lenslet arrays form a stack between a firstsurface facing the object and a second surface facing the image. Thelenslet channels extend further from the optical axis at the firstsurface, and closer to the optical axis at the second surface, therebyproviding demagnification of the object at the image. Such an aspect caninclude a solid state focal plane at the image plane which issubstantially perpendicular to the optical axis so as to receiveelectromagnetic radiation from the object.

In still another aspect, the lenslet arrays form a stack between a firstsurface facing the object and a second surface facing the image. Thelenslet channels extend further from the optical axis at the secondsurface and closer to the optical axis at the first surface, therebyproviding magnification of the object at the image.

In accord with the invention, the lenslet channels typically have clearaperture diameters of between about 5 μm and 1000 μm. As shown herein,certain experimentation was conducted with clear apertures of about 168μm.

In another aspect, the stack can include a macrolens--i.e., a lenselement that is substantially larger than any of the lenslets--that isarranged between at least two adjacent arrays. The macrolens isincluded, generally, to add optical power between the object and image.

To effect continuous imaging, in another aspect, a plurality of lensletchannels are arranged so as to contribute to each point in the image. Inorder to provide an erect image, the SAM must have 2n+1 internal images,where n is an integer.

Lenslet arrays can be constructed and arranged according to theinvention to provide a magnification ratio of less than about 8:1between the object and the image. A second stacked array magnifier canthus be used, in sequence, to provide secondary magnification of theobject to a secondary image along the optical axis. The second SAM issubstantially similar to the first SAM, though the magnification neednot be the same. In this manner, a magnification from each SAM ismultiplied--e.g., 8:1×8:1, which provides an overall magnification of64:1.

In other aspects, the SAM is transmissive to visible electromagneticradiation between about 400 nm and 750 nm. As such, a CCD array can beconveniently arranged at the image and substantially perpendicular tothe optical axis so as to collect the visible electromagnetic radiationfrom the object. However, SAMs of the invention can be made to functionwith any range of wavelengths, such as the ultraviolet and infrared.

For example, the SAM can also be made transmissive to infraredelectromagnetic radiation; and can include "uncooled" microbolometerarrays or other IR detectors, e.g., HgCdTe, at the focal plane. Inanother aspect, the lenslet arrays are made transmissive to visibleelectromagnetic radiation between about 540 nm and 580 nm, whichcorresponds to certain phosphor display devices in the medical arts.Accordingly, the SAM material is optimized in transmission anddiffraction features within the wavelength of interest. Note that thenon-refractive lenslets have greater efficiency for a smaller wavebandwhen optimized to that waveband. By way of example, those skilled in theart should appreciate that non-refractive lenslet arrays which includeblaze grating features have the best efficiency at the designedwavelength. Blaze gratings can be optimized in angle to provide peakdiffraction efficiency, for example, at phosphor emission wavelengths.

To restrict the FOV and to reduce cross-talk, at least one refractivelenslet array of the invention can operate to form an intermediate imageof the object and within the SAM. A field stop is then located at theintermediate image--or very near to the image--to limit the field ofview of one or more lenslet channels. Similarly, a Lyot stop can belocated at the intermediate image to reduce cross-talk from out-of-fieldradiation (preferably, the stop reduces stray light cross-talk to lessthan about 10% of all of the electromagnetic radiation transmitted fromthe object and to the image). To be most effective, the stops should bewithin about a blur distance from the internal SAM image, whereby thedefocus wavefront error is less than about 1/4λ.

In a preferred aspect of the invention, each lenslet channel includes anarray of three lenslets at each lenslet array. These three lenslets aretransmissive to a unique RBG color such that substantially any color canbe transmitted along each channel. At the same time, each of thenon-refractive lenslets are preferably optimized for optical efficiencycorresponding to the RBG color associated with its channel.

The invention also provides for interlaced imaging, or for pixelatedimaging so as to produce an array of discrete images of the object. Inthis latter aspect, the FOV of each channel is substantiallynon-overlapping with adjacent channels to accommodate efficient discretecollection by a solid state sensor.

The lenslet arrays of the invention can also include, in another aspect,one or more optical coatings to improve optical transmission through oneor more lenslet channels.

In one aspect, a SAM is constructed and arranged so as to have anoverall f-number that is less than any of the lenslet f-numbers. Forexample, if each of the lenslet channels is constructed and arranged soas have an f-number of f/1 or greater, the overall f-number of themagnifier is less than about f/1.

In yet another aspect, the SAM of the invention can include means forcreating diffraction orders of electromagnetic radiation transmittedbetween the object and the image, the orders being sufficient to providegreater than approximately 90% efficiency. Similar means can also beincluded to improve the imaging resolution within the image with amodulation transfer function of greater than about 10% at imagefrequencies greater than about 500 lp/mm.

In certain aspects, lenslets of the invention can include refractivesurfaces with aspheric shapes. In other aspects, means for reducingdistortion is included such that the image distortion is less than about2%. By way of example, the distortion reduction means can include edgelenslets having more or less power than other lenslets within the samearray. These edge lenslets are adjacent to one or more edges of themagnifier so as to compensate for pincushion, barrel or petzvaldistortion.

The invention also provides for certain improvements in a method ofmanufacturing a microlenslet array of the type having a plurality oflenslets formed within a optical substrate having a first planarsurface, a second planar surface, and a normal vector that issubstantially perpendicular to each surface. Specifically, theimprovement of the invention includes the steps of forming a firstlenslet array within the first surface, forming a second lenslet arraywithin the second surface, forming a plurality of lenslet channelsbetween the lenslet arrays wherein each channel includes one lensletfrom each of the arrays, the lenslet channels between at least twoadjacent arrays having a channel axis vector relative to the normalvector such that the cross product between the channel axis vector andthe optical axis vector is greater for lenslet channels further awayfrom a line extending along a center of the substrate and parallel tothe normal vector.

In another aspect, a method of manufacturing a microlens stack isprovided for producing a magnified image of an object along an opticalaxis, including the steps of: combining at least two refractive lensletarrays with at least one diffractive lenslet array to form a lensletarray stack with a plurality of lenslet channels, each of the channelshaving a sloped axis between at least two of the arrays, and arrangingthe channels such that the cross product between the sloped axis and theoptical axis is greater for lenslet channels further from the opticalaxis as compared to lenslet channels closer to the optical axis, therebyachieving the magnification selectively.

Such a method can include, in another aspect, the step of arranging thechannels such that at least two channels contribute to the image of eachpoint of the object, providing continuous imagery. The method can alsoinclude the step of arranging at least one array so as to produce anintermediate image of the object and between other arrays, and insertinga field stop at the intermediate image so as to reduce the field of viewof at least one channel.

In still another aspect, a tiled array imager is provided for generatingan image of an object along an optical axis between the object and theimage. To form the tiled array, at least two stacks are arrangedsubstantially perpendicular to the optical axis. Each of the stacks areformed of a plurality of lenslet arrays including one or morenon-refractive lenslet arrays and one or more refractive lenslet arrays.Each lenslet array within a tiled array acts substantially in concert asa single lenslet array; and the tiled arrays form a plurality of lensletchannels. Each of the channels between at least two arrays has a channelaxis with a predefined slope relative to the optical axis. The lensletchannels further from the optical axis have a larger slope than lensletchannels closer to the optical axis. These slopes providingdemagnification between the object and the image.

The invention also provides for scene generating apparatus, including: acomputer for generating signals representative of an selected pattern; aflat panel display responsive to the signals to display the pattern, thedisplay having a display center and a normal vector perpendicular to aface of the display means; a plurality of lenslet arrays formed into astack having a plurality of lenslet channels, the channels between atleast two arrays having a sloped channel axis relative to the surfacenormal vector, the lenslet arrays being constructed and arranged togenerate an image of the pattern on the display means, the cross productof the sloped channel axis and the surface normal vector being largerfor channels further from the center as compared to channels doser tothe center wherein selective magnification of the image is achieved.

In another aspect, a digital camera is provided, including: afilm-formatted camera body and camera lens which generate an image of ascene at an image plane within the camera body and in a formatcorresponding to 35 mm film; one or more non-refractive lenslet arraysand one or more refractive lenslet arrays are formed into a stack with afirst outer surface and a second outer surface, the stack beingconstructed and arranged to fit with the camera body, the lenslet arraysforming a plurality of lenslet channels which act in concert to form asecondary image of the camera's first image that is sized to a solidstate focal plane array; and a solid state focal plane array arranged atthe secondary image.

In yet another aspect, a digital camera is provided, including: a solidstate imaging device of the type that includes an array of detectorpixels responsive to electromagnetic radiation within a range ofwavelengths; a window for protecting the device and for imaging theradiation onto the device, the window having one or more non-refractivelenslet arrays and one or more refractive lenslet arrays formed into astack, the stack being constructed and arranged over the device andforming a plurality of lenslet channels which act in concert to form animage that is sized to the device.

The invention also provides a compact optical correlator for imaging anobject to a solid state detector, including: a first stack and a secondstack arranged substantially perpendicular to an axis formed between theobject and the detector, each stack having one or more non-refractivelenslet arrays and one or more refractive lenslet arrays, the lensletarrays forming a plurality of lenslet channels wherein each channelincludes one lenslet from each of the other arrays, the first stackgenerating a Fourier image between the first and second stacks at afiltering plane, the second stack generating an image of the Fourierimage such that the object is reimaged onto the detector; and an opticalfilter arranged at the filtering plane for selectively filteringelectromagnetic energy so as to achieve selected optical processing.

In one aspect of the invention, a lenslet array stack is integrated withother like lenslet array stacks in a seamless tile so as to achieve alarge format display. Each stack includes at least one refractivelenslet array and at least one non-refractive lenslet array. The stacksare abutted in a manner which achieves the size of the desired largeformat display; the abutted stacks thus functioning, substantially, as asingle stack. At the point of intersection between adjacent stacks, theindividual stacks provide substantially 100% fill factor; and thus theintersection is substantially unnoticeable.

By way of example, advancements in microelectronics manufacturingtechnology have recently produced miniature FPDs with relatively lowcost, and high quality, resolution and yield. These miniature FPDstypically have pixel clear aperture sizes of about twenty-five micronsand an overall dimension of 12.7 mm by 12.7 mm (standard LCD pixelsizes, by contrast, are typically about two hundred and fifty microns,or one hundred dots per inch). They are used, for example, withinhead-mounted displays for defense and commercial applications. Theminiature FPDs offer high optical performance and good contrast withabout twenty to forty lines-per-mm resolution. In accord with one aspectof the invention, an array of miniature FPDs are tiled into a larger FPDof selected size. One or more lenslet array stacks are thus arranged soas to reimage and magnify the tiled FPD into a large format display. Inone practical aspect, the stacks too are tiled. Accordingly, the tiledstacks and the tiled miniature FPDs provide a convenient and efficientlarge format display of minimal thickness and with substantiallyseamless effects caused by the tiling. The FPD is thus scaleable,according to the invention, in a flexible, low cost, high performanceassembly.

Lenslet array stacks of the invention can provide selectivemagnification, as discussed herein. Like magnification stacks can alsobe arranged, in sequence, to achieve integer multiple magnificationsbetween an object and image. Accordingly, and in another aspect of theinvention, one method of the invention is to provide a magnification ofn*M, wherein n denotes the number of lenslet array stacks, and where Mdenotes the magnification of the stack in the sequence.

The lenslet arrays of the invention can be formed in optical gradepolymer, fused silica, quartz, sapphire, calcium, fluoride, opticalgrade glass, silicon, germanium, gallium arsenic, silicon carbide, zincsulfide, zinc selenide, and other glass or crystalline materials thattransmit ultraviolet, visible or infrared light with low absorption andhigh efficiency. Certain polymers, gels and other organic materials canalso be used, such as bacteriorhodopsin, as known to those skilled inthe art.

The invention provides several advantages and has widely varying uses.It provides, for example, hybrid diffractive-refractive opticalmagnifiers for use in optical display and imaging systems, e.g., flatpanel displays, classical cameras, and medical imagers. In one practicalapplication, the invention has beneficial use in bridging 35 mm filmtechnology to the digital age by conveniently reformatting the classicalimage plane to the industrial sizes of the modern day solid-statedevices. In the realm of Fourier and/or digital systems, the inventionfurther provides a convenient forum from which to implement a variety ofoptical correlation or processing techniques, including Fourierprocessing, optical computing, and data transmission methods. Certainother applications, aspects and advantages are realized by theinvention, including:

(1) Hybrid lenslet arrays (i.e., lenslet arrays made from refractivelenslets and at least one array of non-refractive lenslets) of theinvention can provide selective magnification of miniature flat panelelectronic displays. These arrays form a system that exploits theadvances made in microelectronic packaging and manufacturing so thathigh resolution active matrix displays are available at high yield andlow cost. Such a system further enables a large visible field with ahigh fill factor (i.e., high throughput and "frameless" operation sothat the joint between adjacent stacks in a tile are unnoticeable) andyet with low overall weight, size and complexity.

(2) Hybrid lenslet arrays according to the invention are generallyscaleable such that stacks of adjacent arrays perform like functions soas to provide a combined effect with reduced overall manufacturingcomplexity. For example, a hybrid array with an achieved magnificationof two hundred percent can be combined with a similar array to achievean overall object-to-image magnification of four hundred percent. Thisobviously permits the simultaneous and simplified manufacture of likearrays along a common manufacturing line, which lowers cost and whichincreases production yield.

(3) Because of the high resolution and low weight provided by a systemof the invention, hybrid arrays of the invention are particularly suitedto avionic displays; optical systems at command and control centers;high definition television (HDTV); passenger, conference and stadiumdisplays; virtual conference centers; and active billboards.

(4) A hybrid lenslet array forming a stack according to the inventionpreferably has precise registration along the individual lensletchannels defined by the stack transfer, transform or optical radiationtransfer from object space to image space. This provides accuracy incharacteristics of image quality, optical computing and processing.

(5) A stack of microlenslet arrays according to the invention canprovide either magnification or demagnification for a variety ofspecific applications.

(6) Microlenslet surface structure, according to the invention, can be(a) refractive, (b) diffractive kineforms, (c) high order, highefficiency diffractive steering or focusing lenslets, (d) holograms orholographic lenslets, (e) computer generated holograms, (f) effectiveindex modulating surface arrays, (g) apodizing or other spatial filters,and arrays of stops, or (h) other features typically generated bylithographic and semiconductor fabrication technology.

(7) In accord with the invention, hybrid lenslet arrays are formed intoa stack--a process sometimes denoted herein as "hybridization"--ofdifferent surface types (refractive and diffractive in nature) toprovide excellent color, aberration or other correction for highefficiency, high Modulation Transfer Function (MTF) and uniformity overa large aperture optical system.

(8) When combined with a mechanical support structure, the input and/oroutput surfaces of a stack provide a clear aperture which is at leastequivalent to, or greater than, the mechanical aperture of the supportstructure. This permits seamless, or "frameless," tiling of a pluralityof stacks into an infinitely scaleable, tiled, massive parallelprocessed array for very large display or image acquisition over a largefield of view. "Massive parallel processing;" as sometimes referred toherein, means the parallel addressing and control of solid state deviceslike the. CCD and frame readout for the tiled imaging or FPD projectionsystem constructed according to the invention. Massive parallelprocessing effects simultaneous activation or control of tile elementsfor real-time applications (i.e., many frames per second). By way ofexample, if control and readout electronics were serial, as opposed toparallel, then the screen or refresh rates can extend an unreasonableperiod of several minutes.

(9) Microlenslet fabrication of an array of stacks, e.g., to form a tileand/or to achieve integer and repeated magnification effects, permitsthe cost effective manufacture of large scale assemblies. By way ofexample, massive parallel processing of discrete tile subassembliesallows for cost effective computer control of large scale, seamlesslytiled array systems and at very large speeds such as real-time videorates or faster.

(10) A lenslet array, according to the invention, can includemacroscopic planar or refractive lens surfaces in addition to themicrolenslet surface structures. Such a lenslet array can providemacroscopic radiation transfer according to a first purpose, and lensletchannel radiation transfer according to a second purpose. In addition, alenslet array of the invention can and usually does include interstitialplanar microsurfaces, arranged between adjacent lenslets, that do notgenerally contribute to the overall optical throughput from the objectto the image.

(11) In certain aspects of the invention, a stack of hybrid lensletarrays are arranged to efficiently reimage a discrete pixelated objectinto a discrete pixelated image. Alternatively, such a stack can bearranged to image an object into a continuous image--without darkspaces, gaps or blurred regions between adjacent pixels or local imageareas at the image plane--by careful image interlacing of adjacentchannels or kernels of channels in the stacked array structure.

(12) Image interlacing of adjacent lenslet channels provides a uniform,high efficiency optical tile system with a total optical path length orworking distance which scales with the size and f-number of thechannels. This provides for a flat panel optical system with athickness, weight and mass that is smaller than that which is typicalfor a conventional macroscopic lens or mirror optical system.

(13) The lenslet arrays of the invention can be represented by a uniformarray of lenslets of equal surface figure at regular spaced intervals,or by kernels of subarray lenslets of equal surface figure at regularspaced intervals, or by uniquely different lenslets at regular orirregular spacing. In certain aspects the lenslet arrays can be formedof lenslets with varying distance from adjacent lenslets dependent upona location from an optical or mechanical center of the lenslet arraysurface. In yet other aspects, the lenslet arrays are arranged in aradially symmetric fashion, in a mainer easily defined by the Cartesiancoordinate system, or in another group symmetry.

(14) The microlenslets of the invention can have circular, square,hexagonal or other regularly shaped apertures which are equal to orsmaller to the lenslet-to-lenslet center spacing (i.e., so as to providea zone, between lenslets, that does not transfer radiation along alenslet channel). Nevertheless, lenslets are usually circular in shape.

(15) The microlenslets, the microlenslet surfaces, and/or the spacesbetween adjacent lenslets can contain hard stops, masks or opaque zonesto achieve one or more of the following: to control crosstalk, toeliminate or reduce stray light, to reduce image artifacts andaberrations, to maximizing image contrast, and to optimize MTF.Intra-element stops or opaque zones can be fabricated by chemicalmodification of the lenslet array substrate material, by trench etching,and by thermal or other physical processing. Surface stops can befabricated using physical deposition, chemical modification, printing orother process for depositing or placement of opaque material in theinterstices between lenslets. Inter-element stops can include a metal orother opaque mask which also provides for accurate spacing and precisionas to the location of adjacent arrays in the stack.

(16) A hybrid lenslet stack of the invention provides magnification ordemagnification, in one aspect, by outward or inward tilting of lensletschannels relative to an optical axis. In another aspect, the stack canalso utilize microlenslet array channels to effect magnification ordemagnification by outward or inward steering of individual lensletchannel axes. Further, magnification (or demagnification) can be dividedequally or unequally between arrays within a stack, or between stacksarranged as a sequence of stacks in a single optical train.

(17) In the case of pixelated objects or images, individual lensletapertures can be smaller than, equal to, or larger than the pixelateddimensions of the object or image. Lenslet apertures which are largerthan the pixel dimensions of the object or image can have (a) fields ofview covering a plurality of the pixels in object or image space, or (b)a field of view which exceeds the aperture of the lenslet with potentialoverlap among the fields of view of multiple lenslet channels. Lensletsapertures that equal the pixelated dimensions in object space can (a)transfer the image of many object pixels or just one object pixel, or(b) have field of view equal to the lenslet aperture dimension. Lensletswith apertures that are smaller than the pixelated object and/or imagedimensions can utilize or interlace the images of a plurality oflenslets so as to image one point in object space to one point in imagespace.

Lenslets which have an aperture that equals the field of view are theleast preferred configuration due to the extremely tight tolerancerequired in fabrication, registration, and the low defect densityrequired to achieve uniform image transfer. Lenslets with apertures thatare larger than the lenslet's field of view require simpler masks forfabrication with reduced features; but defect densities can not betolerated unless multiple lenslet channels are used to image a singlepoint in object space to image space. Lenslet arrays with small aperturesizes, relative to the lenslet's field of view, require the mostcomplicated masks for fabrication and the lowest packing fraction foroptical efficiency; but also allow for the greatest tolerance inregistration and defect density due to the interlacing of images frommany channels from a single object point.

(18) Hybrid lenslet array stacks according to the invention can provideinverted or erect images. Systems with erect images require an oddnumber (i .e., 1, 3, 5, . . . or 2n+1, where n is an integer number) offield stops or field image surfaces internal to the stack structure.Systems with an inverted image output can have either zero or an evennumber of field stops or field image surfaces internal to the stackstructure. Stacks with internal field images can incorporate field stopsin the form of micromachined, electro-formed, molded or other apertureplates for aberration control or the improvement of image quality (e.g.,MTF).

(19) Stacks constructed according to the invention generally include, atleast, four lenslet array surfaces and two substrate elements. The stackcan be assembled as a stack of discrete air-spaced elements withexternal mechanical fixturing or with mechanical spacers placed betweenthe elements and arrays. Such a stack provides a stable, monolithicstructure which easily integrates into a system, device or product.

Stack surfaces and/or spacers can include fiducial marks to facilitatemicron-level registration and location of components. These fiducialmarks can be deposited, or male or female patterns can be etched into,surfaces at interstices between microlenslets. The opposing surface orfiducial mark of the next element or spacer between elements can alsohave fiducial marks or a mating surface relief pattern to facilitateassembly and co-location of elements and components of the assembly.

Alternatively, the lenslet apertures can be register into one or moremask plates between adjacent elements of the stack to provide forco-location and precise positioning in x-, y- and z-axes of the hybridstack. Monolithic, self-alignment construction of stack assembliesallows for compact, high performance optical systems with superiorstructural and environmental integrity in comparison to conventionaloptical systems. Stack optics can also be assembled with buried andcemented surfaces for added reliability and impermeability tocontamination or dirt.

(20) Multi-element stack optical systems of the invention with one ormore intermediate image planes facilitate the insertion of passive oractive media at a field image or at a collimated space between twolenslets in the stack. Active media located at the field stop provides aconvenient forum from which to accomplish optical processing, and caninclude: electro-optic modulators, liquid crystal light valves, activecolor filter mosaics, other spatial light modulators, computer generatedholograms, and even gain media to accommodate a wide variety ofapplications for optical transform systems, compact optical correlators,optical network and computing systems, switching systems and numerousother optical signal processors. Fixed passive spatial filters, colorfilters, or encryption filters can also be colocated at a field image inthe stack assembly to create a wide variety of fixed or passive opticalsignal processing systems. Again, the compact, monolithic nature of thestack assembly allows for ease of assembly and integration with internaldevices, associated electronics and mechanical fixturing.

(21) Stack components and assemblies can be fabricated using a widevariety of materials and methods compatible with volume microelectronicsassembly tooling and equipment. Substrates can be semiconductor, glass,single crystal, polycrystalline, liquid crystal, polymer or otheroptically transmissive material amenable to processing into microlensletarrays. Metal or other solid negative masters can be used for moldfabrication of hybrid lenslet arrays and stacks. Hybrid arrays can alsobe cemented to bury surfaces for added reliability. Spacers betweenelements can be glass, metal, polymer, crystalline or other appropriatestructural or optically opaque medium to facilitate registration and toenhance optical and mechanical properties. Active and passive deviceslocated between elements, particularly at field image planes, canfurther incorporate electronics and mechanics for assembly and fixturingof stacks and lenslet arrays.

(22) Stacks and lenslet arrays of the invention can apply toapplications across the optical spectrum, from the deep ultraviolet tothe far infrared. Indeed, many semiconductor materials that facilitatemicroelectronic fabrication processing have excellent infraredtransmission properties so as to support infrared applications. Thecompact, flat panel nature of the stack optical system allows for easyintegration with an image plane device such as a focal plane arraydetector. The stack optics can also function as an optical signalprocessing window which isolates and protects the FPA device in aprotective atmosphere, or in a controlled environment atmosphere such ascryogenic or other thermally controlled environment (e.g., heated,isothermal, and non-cryogenic-cooled).

(23) The stack assembly, according to the invention, provides a singleoptical assembly for use in imaging, display or detection applicationsusing a single flat panel display, focal plane array, other directdisplay device or detector device. The ability to fabricate stack opticswith nearly 100% clear aperture (relative to the mechanical size of thestack) allows for infinitely scaleable tiling of massive parallelprocessed arrays for very large flat panel displays or wide area, highresolution image acquisition systems.

(23) In addition to the applications discussed herein, the invention isparticularly well suited for application with (a) massively parallelprocessed tiled large area FPD systems, (b) massively parallel processedlarge area real-time medical imaging systems, (c) compact opticalcorrelators, (d) compact IR FPA imaging cameras with an integral coldstop, (e) compact CCD imaging systems, and (f) optical encryptionsystems for security applications.

The fabrication of a stack or SAM assembly according to the inventionhas many aspects, including:

(24) The lenslet arrays of the invention can be manufactured by moldingan optical grade polymer, or by coextrusion of an optical polymer, withan opaque polymer. In one aspect, the mold is fabricated from a negativerelief of the refractive and non-refractive lenslet surface features,plus fiducial marks and mechanical assembly features. The negativerelief is then fabricated into a metal, ceramic or high temperaturecomposite master, which is produced by micromachining or by directforming into the master mold material. In another aspect, the mold isproduced in an iterative manner by transferring a positive master inglass, semiconductor or crystal material to a ceramic or elastomertemplate, which creates the negative mold master.

(25) The arrays of the invention are made from a variety of substratematerials. Depending upon the wavelengths of operation, the substrateswithin a particular stack can be made from one or more differentsubstrate materials so as to correct for optical color or to accomplishdifferent distributions of optical power within the stack.

(26) Lenslet arrays of the invention can also be manufactured throughreplication. In this aspect, a mold is fabricated from a negative reliefof the refractive and non-refractive lenslet microsurface features, aswell as of the fiducial and mechanical assembly features. Preferably,the negative relief is fabricated into a metal, ceramic or hightemperature composite master, which is produced by micromachining or bydirect forming into the master mold material. The master is thereaftercoated with a release agent followed, for example, by (a) an epoxy, (b)a polymer, (c) an optical quality organic, or (d) a sol gel material toproduce a thin sheet of material with lenslet array features, fiducialmarks, and mechanical assembly features to facilitate transfer andbonding to a flat optical substrate. The bulk optical substrate canadditionally include opaque interstitial areas or masks to provide forstops and to eliminate or reduce optical crosstalk among nearby lensletchannels.

(27) Fabrication of lenslet arrays according to the invention canbeneficially utilize substrates, equipment and process technology commonto semiconductor microelectronic lithography. These semiconductorprocesses can include deposition and photoresist mask generation tofacilitate the fabrication of surface features, the modification of theindex of refraction, and the application of physical masks. Reactorprocesses common to semiconductor processing are also used, in otheraspects, for chemical etching, reactive ion etching, plasma etching,physical vapor deposition, chemical vapor deposition, epitaxial growth,ion implantation, electron beam deposition, and other radiation exposureand activation processes to form refractive and non-refractive lensletarrays with the selected substrate material.

(28) The interstitial regions between lenslet channels are preferablycoated with an opaque material--such as metal, ceramic or oxide--usingsemiconductor microelectronic processes, particularly the reversal ofthe photomask resist process described above in paragraph (27).

(29) In a preferred aspect of the invention, the masks used to fabricatethe lenslet arrays include fiducial features, which facilitate alignmentand registration of lenslet array channels in Cartesian x-y androtational coordinates. The fiducials are either located outside of thelenslet clear aperture or interstitial to the lenslet array features.These fiducials can be clear with an opaque background, or opaque in atransparent background.

(30) The fiducial features of the invention can frame the entire lensletarray mask, or parts of the lenslet array mask, or within interstitialregions to the lenslet array channels. Fiducials can be horizontal orvertical lines, sequences of lines, crossed lines, circles, squares,hexagons, other geometries or combinations of geometric shapes.

(31) Generally, the fiducial markings facilitate the manufacture ofprecise registration of photomasks and lenslet stacks by co-alignmentand/or registration. The markings can also create optical effects toassist in this assembly process. For example, precise alignment of themarks within a substrate and relative to a side-to-side arrangement ofarrays can be made to produce optical effects such as a Moire pattern orother interference effect so as to indicate proper registration.

(32) In a preferred aspect of the invention, lenslet array substratesare fabricated with additional fiducial marks, or surface relieffeatures (etched below the surface or protruding above the plane of thelenslets) to facilitate stack assembly. In particular, these fiducialscan be used to assist in the alignment of elements such as mechanicalspacers between adjacent arrays, or in the positioning of stops oroptoelectronic devices at an intermediate image plane. Their placementcan be outside, or interstitial to, the array's clear aperture; andtheir shape can be in the form of lines, crosses, dots, rectangles,squares or other geometric features that permits visual or machine-aidedalignment of stack elements. The fiducials can further facilitatemechanical pinning or interlocking of adjacent stack elements.

(33) In one convenient aspect of the invention, fiducial marks andassembly features are fabricated of metal or other target materials usedin the masking of the interstitial and surrounding regions of thelenslets. In another aspect, the fiducial marks and assembly featuresare etched into the substrate. In yet another aspect, the fiducial marksand assembly features are fabricated onto mechanical spacers and otherdevices for placement within the stack.

(34) Fiducial marks and assembly features can be formed of solder,thermoset or other material that transforms from a solid to a liquidwhen subjected to heat or other activation such that a surface tensionis created to promote alignment of the stack. The subsequenttransformation of the fiducial and assembly features back to a solidthereby bonds the stack together into a monolithic structure.

(35) The stack can include lenslet surfaces that are immersed in anadhesive for monolithic bonding of the SAM.

(36) Stack assembly with micromechanical and electronic parts is greatlyfacilitated by visual or machine-aided tooling such as a microscope orother imaging devices. Typically, these devices have sufficientmagnification to view the fiducial alignment microfeatures so as tofacilitate precise array positioning in x, y and rotational coordinates.

(37) In another aspect, anaerobic, thermoset, room temperature adhesivesor other bonding agents are used to assemble the stacks at the edges orat internal locations within the stack.

(38) Mechanical spacers and surface alignment features can include agel, thermoset or a solder which bonds the stack together when activatedat the point of proper registration.

(39) Stack alignment features can include thru-holes--at the edge of thestack's clear aperture or at interstitial locations relative to thelenslet channels--so as to provide for the insertion of micromechanicalpins which assist stack assembly and which mechanically tie the stackinto a monolithic structure.

(40) A substrate can include features which are designed into its outersurfaces to facilitate the assembly of the SAM relative to externalmechanical mounts or housing structure. Further, such features canassist in the alignment and placement of an array relative to an imagingdevice, detector, or display device, e.g., a LCD. They can alsofacilitate assembly of a seamless tiled array construction of SAMs intoa massive parallel processing system.

In another aspect, the invention also concerns a hybrid,refractive/diffractive, stacked optical lens array imaging system thattransmit a two-dimensional image from an object plane to an image plane.Specifically, the imaging system utilizes a stack of arrays of lenses,each array comprising a plurality of small apertured lenses("microlenses" or "lenslets"). The optical imaging system includesmicro-optics with a relatively short focal length and high opticalefficiency and high resolution for imaging with or without magnificationor demagnification. The optics thus form a "stack" of a plurality ofhybrid (i.e., refractive, diffractive, etc.) lenslet arrays.

The system can provide for finite conjugate imaging or infiniteconjugate imaging, and contains a least one or more intermediate fieldimages with an erect or inverted image at the overall system outputimage plane. The system can further reimage a pixelated object space toa discrete array image space. The system can also reimage a continuousobject to a continuous image without dark spaces, gaps or blurredregions between pixels or image areas at the image plane.

Each array of lenslets may incorporate integral hard stops (such aschrome baffles) or opaque zones between lenslets for control ofcrosstalk, for minimization of stray light, and for maximization ofimage contrast and the modulation transfer function. A key aspect of thesystem is the interlacing of images from adjacent lenslet channels sothat multiple lenslet channels may contribute to reimaging a point orpixel in object space to a corresponding point or pixel in image space.The effective f-number of the system is therefore smaller than thef-number of a single lenslet channel. The thickness of the system is afunction of lenslet size, f-number and optical lens material, and istherefore substantially thinner than an equivalent optical system usinglarge aperture macrolenses.

The stack of lenslet arrays can be configured and assembled within amonolithic structure for simplicity of construction and alignment. Theimage interlacing property of the system accommodates a large tolerancefor lateral misalignment due to the contribution of multiple lensletchannels to the complete, continuous image.

The number of lenslets in each array stack can be greater than, equalto, or less than the total number of pixels in object or image space.Magnification can be divided equally among the lenslets or in variousportions between the optical stack before and after the field stoparray. Individual lenslets or entire lenslet arrays can be tilted inwardor outward for magnification or demagnification. Lenslet arrays can beformed on planar substrates or can be hybridized with macrolenssubstrates. The lenslet surface figures can be constant over one arraysurface with uniform spacing. In the alternative, the surface figurescan be arranged in kernels of n by m lenslets of constant figure or withchanging figure in the adjacent kernels of lenslets. Or, the surfacefigures can vary step-wise across the entire aperture of the stack suchthat every lenslet has a unique figure unto itself.

The field stop array can incorporate either an array of reticles, aspatial light modulator, or other passive or active optical systems ormedia. The lenslets can be refractive, diffractive, holographicallygenerated, or gradient indexed. The value of hybrid lenslet arrays isfor chromatic correction, aberration correction or possible encryptionto produce a desired corrected or processed image at the image plane.

The excellent uniformity of optical throughput and image quality acrossthe entire clear aperture of the system at the image plane output allowsfor fabrication of "tiles" of the stacks with optics to the edge for100% clear aperture. The tiles can be integrated into a very large,infinitely scaleable imaging or display system in a seamless fashion.For example, in one aspect, a large, high resolution, flat panelelectronic wall display is formed using a plurality of small liquidcrystal displays ("LCDs"), miniature flat panel displays ("FPDs") orother compact displays, magnified and imaged through a mosaic array oftiles. In another example, an ultra-high resolution, large area, chargecoupled device ("CCD") medical X-ray imaging system is formed by tilingstacks with X-ray phosphor screen inputs to small, low-cost, high-speedCCD camera outputs. Massive parallel processors ("MPPs") integratedwithin a high speed computer system permit video rate, real-time, orother high frame and data rate transfer of an image in the case of themedical X-ray system, or active display in the case of the wall display.

The invention is next described further in connection with preferredembodiments, and it will become apparent that various additions,subtractions, and modifications can be made by those skilled in the artwithout departing from the scope of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete understanding of the invention may be obtained byreference to the drawings, in which:

FIG. 1 shows a cut-away side view of a stacked array magnifierconstructed according to the invention.

FIGS. 1A and 1B show, respectively, front and back views of the stackedarray magnifier of FIG. 1;

FIG. 2 shows a system constructed according to the invention and whichincludes a five array stack for imaging an object onto a CCD array;

FIGS. 2A and 2B illustrate representative techniques of the inventionused to separate adjacent arrays to obtain selected separation distancesas well as coregistration;

FIG. 3 illustrates multiplicative magnifications achieved through aplurality of magnifying stacks constructed according to the invention;

FIG. 4 illustrates an arrangement of stacks formed into a tile toprovide a large format display according to the invention;

FIG. 5 illustrates one stack constructed according to the invention andwhich includes both microlenslets and macrolenslet structure;

FIGS. 6A-6B illustrate selected types of imaging according to theinvention, including continuous and pixelated imaging;

FIGS. 7-7E illustrate selected options of arranging microlensletpatterns in an array, according to the invention;

FIGS. 8 and 8A show other techniques of imaging an object withmagnification, according to the invention, and with tilted lenslets orlenslets with varying optical power within the stack arrays;

FIGS. 9 and 9A show a sequence of stacks providing a relay of images toachieve erect or inverted images, selectively, and to stop the internalimages so as to improve image quality;

FIGS. 10A-10C show, respectively, holographic lenslet manufacture, arepresentative holographic lenslet, and a resulting operation of such aholographic array, in accord with the invention;

FIGS. 11A-11B show, respectively, phase modulation lenslet manufactureand a resulting operation of a phase modulation array, in accord withthe invention;

FIGS. 12A-12C show, respectively, index modulating lenslet manufacture,a representative gradient index lenslet, and a representativeGaussian-shaped index lenslet, in accord with the invention; and FIG.12D shows an alternative index modulation lenslet manufacture utilizingnanometer-sized substrate cuts;

FIGS. 13A and 13B illustrate, respectively, a negative mold and alenslet array made from the mold, in accord with the invention;

FIGS. 14A and 14B illustrate lenslet structures made from diffractivekineforms;

FIGS. 15A-15G illustrate different lenslet constructions according tothe invention;

FIGS. 16A-16C illustrate different lenslet FOVs relative to an RGBobject, in accord with the invention;

FIGS. 17A-17B illustrate how lenslet FOV impacts image defects;

FIG. 18 shows a cut-away side view of a stack assembly constructedaccording to the invention and including spacers, fiducials, assemblypins, opaque stops at the interstitial spacing, and associated items;

FIG. 19 illustrates a Hartman Transform encoder constructed according tothe invention;

FIG. 20 illustrates optical processing apparatus constructed accordingto the invention;

FIG. 21 illustrates a scene generation system constructed according tothe invention;

FIG. 22 shows a digital camera constructed according to the invention,including a solid state display and a stack for converting a 35 mm filmimage to the solid state display;

FIG. 23 is a schematic view of a four element stack of the presentinvention;

FIG. 24 is a schematic view of a four element stack similar to that ofFIG. 23, incorporated into an embodiment for magnification of lightemitted from a miniature flat panel display, in accord with theinvention;

FIG. 25 is a schematic diagram of the system of FIG. 24 incorporatedinto a computer-controlled, multi-stack embodiment of the invention;

FIG. 26 is a schematic view of a four element stack, similar to that ofFIG. 23 and FIG. 24, incorporated into an embodiment of the inventionfor demagnification of X-rays to a charge coupled device; and

FIG. 27 is a schematic diagram of the system of FIG. 26 incorporatedinto a computer-controlled, multi-stack embodiment of the invention.

DETAILED DESCRIPTION OF THE DRAWINGS

FIG. 1 shows cut-away side view of a stacked array magnifier 10constructed according to the invention. The "stack" of FIG. 1 is madefrom two substrates 12 and 14 held together by a opto-mechanical fixture16. Each of the substrates 12, 14 has at least one microlenslet array 18disposed therewith. As illustrated, for example, substrate 12 providestwo arrays 18a, 18b; while substrate 14 provides two arrays 18c, 18d.Each of the arrays 18 is made up of a plurality of microlenslets 20, thephysical features of which are described in more detail below. Briefly,however, there are at least two types of lenslets 20 in the magnifier10: refractive lenslets and non-refractive lenslets. As illustrated, forexample, array 18a and array 18d are made up of refractive lenslets 20aand 20d, respectively. Array 18b and 18c, on the other hand, are made upof non-refractive lenslets 20b and 20c, respectively. Typically, thenon-refractive lenslets are made up of diffractive gratings whichinclude blazed grating microfeatures.

The magnifier 10 of the illustrated embodiment operates to form an image22 of the object 24 along an optical axis 26 (note for purposes ofillustration that the object "H" of FIG. 1 is shown sideways to theimaging axis when, in reality, it would need to face the magnifier 10 inorder to be reimaged).

The lenslets 20 of the arrays 18 make up a plurality of channels 28 (forclarity of illustration, only two channels are illustrated with a dottedline indicating the optical path along the channel). In order to providea magnification in the illustrated embodiment of FIG. 1, some of thechannels are sloped relative to the optical axis 26 and between at leasttwo of the arrays 18. By way of example, the slopes of the channels 28between arrays 20b and 20c vary as a function of the channel's distancefrom the axis 26: the slope of channel 28a which is further from theoptical axis 26--is greater than the slope of channel 28b, which iscloser to the optical axis. Accordingly, the light radiation between theobject 24 and image 22 is "spread out" to achieve the desiredmagnification.

The details of the magnification and imaging process, according to theinvention, are described in more detail below. However, it should beapparent that each of the channels images points of the object 24 topoints in the image 22. For example, channel 28b images point 30 ofobject 24 to point 32 in image 22; while channel 28a images point 34 ofobject 24 to point 36 in image 22. The spacing between lenslets 20 andthe optical character of the lenslets along each channel determines theindividual field of view of each channel 28. As will become moreapparent below, the channel field of view can overlap with otherchannels to provide a continuous image, such as shown in FIG. 1.

Those skilled in the art should also appreciate that the imagingproperties of the magnifier 10 permit a similar demagnification ofobjects by inverting the magnifier 10. If, for example, the image 22 isthe "object," then the magnifier 10 will generate an "image" 24 which isa demagnified version of the "object."

FIGS. 1A and 1B illustrate, respectively, front and back views (not toscale) of the magnifier 10. Specifically, FIG. 1A is a view of themagnifier 10 as viewed from the position of the object 24; while FIG. 1Bis a view of the magnifier 10 as viewed from the position of the image22. As easily seen, the spacing between the various lenslets 20 isgreater within FIG. 1B as compared to the spacing between the lensletsof FIG. 1A, which is a result and a function of the desiredmagnification. Although not necessary, the lenslets 20a of array 18a areillustrated as being smaller than the lenslets 20d of array 18d inproportion to the magnification desired between the object 24 and image22. Usually, and similar to conventional optical lens trains, lensletsof the several arrays are made with identical diameters to accommodatemechanical microfeatures. However, because channels can be tilted (asdescribed herein), inadequate allowance in the interstitial spacing canresult in crowding of lenslets at one of the surfaces. Accordingly, thedesign of a stack such as stack 10 should properly consider a balance oflight collection or transfer efficiency (i.e., the maximum lenstransmitting area or open area ratio through the arrays) whileaccommodating the lenslet channel spacing of all the arrays. By way ofexample, if the last surface--e.g., array 18d--has very small aperturesspaced widely apart, then it is possible to accommodate a largemagnification with close spacing of lenslets at the first surface--e.g.,array 18a. However, the low open area ratio of the second surface willresult in a low optical efficiency, similar to the effect of stoppingdown a conventional camera (which is good for high speed applicationsbut only if there is good lighting, e.g., a flash lamp). Typically, thelenslet sizes are between about 5 μm and 1000 μm.

In FIGS. 1A and 1B, the area illustrated with diagonal lines (denoted inthe figure as "interstitial planar microsurface) and between the severalthe lenslets 20 is generally planar and does not function to imageradiation between the object 24 and image 22. Rather, the energy whichimpinges between lenslets 20 is preferably blocked so that suchradiation does not reach the image plane (i.e., the plane at which image22 resides). As described below, baffling, stops, masking and otheroptical techniques are used to prevent this unwanted radiation transfer.In one example, the interstitial planar surface is itself coated to beoptically opaque to the desired radiation transmitted between the object24 and image 22. In other examples, the opaqueness between lenslets canbe fabricated by chemical modification of the lenslet array substratematerial, by trench etching, and/or by thermal or other physicalprocessing. Surface stops forming the opaqueness can also be fabricatedusing physical deposition, chemical modification, printing or otherprocesses.

Stops such as a field stop or a Lyot stop can also be inserted at ornear to an internal image to reduce cross-talk or other stray radiationthat might scatter from various surfaces or which might transmit throughthe interstitial surfaces. With further reference to FIG. 1, forexample, the stops 25 are arranged at an intermediate image plane 27within the stack (note that at least one intermediate image is requiredto achieve an upright image 22). Those skilled in the art willappreciate that the purpose of a field stop, generally, is to restrictthe field of view; while a Lyot stop is used generally to limit thetransmission of unwanted diffraction effects. These inter-lenslet stops25 can include a metal or other opaque mask which also provide foraccurate spacing and precision as to the location of adjacent arrays 18in the stack. They further can be arranged into a single structure suchas a flat metal disc that is mounted to within the fixture 16 via amale/female connection 29 into the fixture 16. Note, for clarity ofillustration, that only two stops 25 are shown when it is intended thatmany or most of the channels 28 have corresponding stops 25 located atthe image plane 27.

Generally, at least four arrays of lenslets and at least two substratesare used to form a stack according to the invention. FIG. 2, forexample, illustrates one simple use of the invention: a four substratestack of five arrays imaging an object 38 onto a solid state device suchas a CCD array 40. CCD electronics 42 and known to those skilled in theart transfers the charge data from the CCD array 40 to a computer 44with a display screen 46 so that the object's image 48 is viewable onthe screen 46. In this illustration, all of the channels 50 aresubstantially parallel to the optical axis 52 such that unitmagnification is achieved (i.e., unit magnification means amagnification of "1").

With further reference to FIG. 2, a stack 53 is made of four substrates54a-54d that each have one or more arrays of lenslets 56 added thereto(note, for clarity of illustration, that only four lenslets are shownper array while in reality many lenslets exist for each array).Substrate 54a has one array disposed internally to the substratematerial, which is typically made from semiconductor material, glass,single crystal, polycrystalline, liquid crystal, polymer or otheroptically transmissive material amenable to processing into microlensletarrays. In one example, the lenslet 56a of the array within substrate54a is made through ion doping to achieve a refractive effect, such asdiscussed in connection with FIGS. 11 and 12. Substrate 54b andsubstrate 54c each provide an array of non-refractive lenslets 56b and56c, respectively, that are made onto the surfaces of the substrates54a, 54b. Substrate 54d has two arrays formed onto each of its surfaces:an array of non-refractive lenslets 56d on one surface of the substrate54d and an array of refractive lenslets formed onto the other surface ofthe substrate 54d.

FIG. 2 also illustrates other methods of mechanically holding thesubstrates 54 and arrays lenslets 56 into the stack 53. Like in FIG. 1,one method for holding the arrays together is with an opto-mechanicalfixturing 58 attached to the edges 60 of the substrate arrays 54.However, the arrays can also be separated by spacing elements 62. In oneembodiment of the invention, fiducial marks 63 are made onto one or moreof the surfaces (through deposition or other methods known to thoseskilled in the art of microlenslet manufacture) so that the elements 62can be properly placed between the interstitial spacing between thelenslets. Such spacing elements 62 can further support the accuratecoregistration of adjacent arrays, such as illustrated in FIGS. 2A and2B.

FIG. 2A illustrates portions of two substrates 64 and 66 separated byspacing elements 68. Not only do the spacing elements 68 provide properdistancing between the arrays 70a, 70b, formed by the lenslets 72a, 72b,respectively; but they also provide for proper coregistration betweenlenslets 72 within any given channel 74 since the female etch patterns76 are accurately applied to the substrates 64, 66 prior to assembly ofthe stack.

FIG. 2A also illustrates one non-refractive lenslet 72b constructedaccording to the invention. The lenslets 72b are microelements whichform an array of blazed gratings. Those skilled in the art shouldappreciate that blaze gratings have angled grating grooves 73 that areoptimized, in angle and as a function of wavelength, so as to diffractlight energy into highly efficient orders and in the direction ofchoice. The grooves 73 can be tilted at an angle θ, for example relativeto the substrate surface 66a, so as to achieve the desired opticalenergy transfer. Representative designs according to the invention aredescribed in more detail below.

The combination of a non-refractive lenslet 72a and non-refractivelenslet 72b in a stack is sometimes denoted herein as a "hybrid" lensletarray. In particular, a stack of different lenslet arrays is ahybridization between refractive and non-refractive lenslets to achieveimproved optical properties such as reduced color or other opticalaberrations, enhanced throughput efficiency, high resolution or MTF, andfield uniformity.

FIG. 2B illustrates yet another embodiment of aligning adjacent arraysin a stack. In particular, FIG. 2B shows partial substrates 78, 80 withpartial arrays of lenslets 82, 84 spaced apart by male and female etchpatterns 86, 88, respectively, formed into the substrate surfaces. Notethat in FIG. 2B the two adjacent arrays of lenslets are all refractiveelements, which is yet another reasonable and expected lensletconfiguration according to the invention.

FIG. 3 shows a sequence of three stacks 90 arranged into an opticalsystem 92 to provide a magnified image 94 of an object 96. By way ofexample, each of the stacks 90 can be made similar to the magnifierstack 10 of FIG. 1. Typically, a stack according to the inventionprovides at most an 8:1 magnification ratio. However, stacks can bearranged in sequence to boost the overall magnification significantly,such as shown in FIG. 3. If, for example, each of the stacks 90 providesa magnification of 2:1, then the sequence of stacks 90 of FIG. 3provides a magnification of 2³, for a total magnification of 8:1 for thesystem 92. As above, one technique for keeping the array of stackstogether is through an opto-mechanical end piece 94. However,inter-stack spacers 96 can also be used alone or in conjunction with thepiece 94. The spacers 96 can be made similarly to the spacers 62 of FIG.2, and including the various arrangements set forth in FIGS. 2A and 2B.Like above, the achievement of precise coregistration between lensletarrays is advantageous in improving image quality and processingcapability.

It is not necessary, however, that each of the stacks 90 of FIG. 3 havethe same magnification. Rather, stacks of different magnification can bearranged in sequence to provide a multiplying magnification effect. Inaddition, magnification limitations of 8:1 are dependent upon manypractical factors relating to lenslet spacing, open area ratios, lensletpowers, and other fabrication and assembly issues. Those skilled in theart should appreciate that the 8:1 ratio will increase with improvementsof microlithography, lenslet processing, and micromachining andmicroalignment.

One dear advantage of the system 92 of FIG. 3 is that each of the stacks90 can be made separately and similarly along a common production line,thereby simplifying the complexity of the overall system 92, improvingproduction yields, and reducing non-recurring costs needed to tool-upfor the desired opto-mechanical configurations.

FIG. 3 also shows the f-number differences between the overall system 92and an individual channel 96. Note for clarity of illustration that onlyone channel 96 is illustrated, with associated lenslets 98; while inreality there are many similar channels arranged throughout the stacks90. In addition, the lenslets 98 are grossly oversized in comparisonwith reality, also for clarity of illustration. It is dear withreference to FIG. 3 that the overall f-number of the system 92,illustrated by the cone angle 100, is less than the f-number of thechannel 96, as indicated by the cone angle 102. Accordingly, thef-number of the channels 96 is less than the f-number of the system 92.Those skilled in the art should appreciate that an f-number of about f/1is desirable in view of energy throughput; and therefore many systemsstrive for similar low f-numbers. As a result, individual channelf-numbers are typically greater than about f/1.

FIG. 4 shows a perspective view of an imaging system 104 made from tiledarray of stacks 106 that are formed together into a two functionalstacks 108a, 108b. It is sometimes difficult to manufacture a singlestack at desired large physical dimensions. Accordingly, stacks can betiled together to the desired display format. As above, they can alsoprovide selected magnification to achieve the desired display size andcharacteristics. By way of example, a stack of the invention can be usedto provide a large format display of a miniature FPD 110. The miniatureFPDs of the prior art have very high quality and resolution; but theyare too small for comfortable viewing. Thus, even though the object 112on the FPD 110 is good; it is too small for viewing by an audiencespaced away from the display 110. Accordingly, the system 104 reimagesthe display 110 (and particularly the object 112 on the display 110) tothe front 114 of the system 104 (see the image 116 of the object 112).In this manner, a user (here shown as a human eye 118) can comfortablyview the image 116 as opposed to the object 112 on the FPD 110.

Because the lenslets (not shown) of each of the stacks 106 are so smalland because they extend substantially to the edge of each stack, thejunctures 120 between the separate stacks are substantially invisible tothe user 118. That is, the lenslets can provide substantially 100% fillfactor of the physical size of the stack; and therefore the joinder oftwo or more stacks in a tile--such as illustrated in FIG. 4--ispractically invisible or "frameless." Accordingly, the tiling processdescribed in FIG. 4 is scaleable to the desired physical configurationof the overall display 104. In the case of massively parallelprocessing, the tiled stacks are arranged in a pattern that is adequateto accommodate the data being processed.

Irregardless of the fill factor, each of the channels passing throughthe stacks 106 has a selected field of view (FOV). If desired, the FOVof each channel can be overlapping with at least one other channel sothat a continuous image is obtainable. This overlapping FOV additionallyhelps mask the junctures 120 from the user 118. The overlapping FOVeffect is sometimes referred to herein as "image interlacing" wherebyeach point on the object is reimaged by a plurality of channels so as toensure a continuous image, such as shown in FIG. 1.

Because the arrays of the invention can have very high fill factorsrelative to the physical dimension of the stack, it is typically themechanical support structure which limits the overall aperture of thestack. By way of example, and with reference to FIG. 3, it is generallythe clear aperture 95 of the structure 94 which limits the aperture ofthe system 92 and not the combined FOV of the lenslet arrays with thesubstrates.

FIG. 5 shows one embodiment of the invention wherein a stack 122constructed according to the invention includes both arrays ofmicrolenslets 124, at least one macrolens surface 126, and one or moresubstrates 128. Opto-mechanical fixturing 130 supports the stack andholds the arrays in alignment. The purpose of the macrolens surface 126is to provide continuous and relatively large optical power to radiationpassing therethrough so as to achieve a desired optical result. Lenslets124 can be made with the macrolens surface 126, as shown, or themacrolens can be free-standing and without lenslets therewith. In atleast one of the arrays of lenslets 124 is non-refractive in nature,such as illustrated by the lenslets 124a on the substrate 128a.Accordingly, the microlenslets 124 of FIG. 5 generally have a firstpurpose directed at microimaging features of the radiation transfer;while the macrolens 126 has a second purpose directed at macroimagingfeatures of the radiation transfer.

FIGS. 6A-6B illustrate various types of imaging achievable with a systemconstructed according to the invention. In FIG. 6A, a stack 132 isconstructed with arrays of microlenslets 134 and channels 136, such asdescribed above (note, as before, that only a few of the microlenslets134 and channels 136 are shown for clarity of illustration). The objectin this figure is a pixelated object array 138 such as a computerdisplay screen, containing a plurality of light emitting pixels 140.Even though the entire stack 132 operates to provide an image 142 (hereshown with slight magnification, though not required) of the array 138,each individual channel's FOV is limited to the pixelated dimensions ofthe computer display pixels 140 such that there is a one-to-onecorrespondence between lenslets 134 and pixels 140; and that there is nooverlapping between channels 136 so that no two channels 136 reimage thesame pixel to the image 142.

The arrangement of FIG. 6A is useful for example when it is important torestrict the cross-talk between adjacent pixels. As shown, the image 142is easily converted to electrical signals by a CCD array since the image142 is also pixelated, magnified, and discrete with a one-to-onecorrespondence with the pixels 140.

Those skilled in the art should appreciate that the FOV of each channelcan thus be arranged to cover less than the x, y pixel dimensions of thearray 138. This might be used, for example, to greatly limit the effectsof cross-talk and scatter between adjacent channels and to compensatefor diffraction effects.

FIG. 6B, on the other hand, illustrates image interlacing such that eachpoint 144 on the object 146 is reimaged to corresponding points 144' atthe image 152 by at least two channels 148 of the stack 150. For clarityof illustration, only two channels 148 are shown in the stack 150, eachchannel having at least one refractive lenslet 153a and at least onenon-refractive lenslet 153b; and only two channels 148 are shown toreimage each point 144 of the object 146 to the image 152. Typically,many more channels 148 reimage each point 144 in the object 146. In thismanner, the image 152 is "interlaced" with microlenslet reimaging frommany channels 148, thereby ensuring that there are no gaps in the image,even if a channel 148 is damaged or inoperative.

FIGS. 7A-E illustrate various arrangements of lenslets within a lensletarray such as described herein. For purposes of illustration, the arraysof FIGS. 7A-7E are shown from a view that is substantially perpendicularto the face of the array, such as along the optical axis 26 of FIG. 1.Briefly, FIG. 7A shows an array 160 of lenslets 162 arranged atregularly spaced--e.g., Cartesian--intervals 164 along the array surface166. FIG. 7B similarly shows a kernel array 168 of lenslets 170 withselected distances 172 between lenslet kernels 168 (i.e., a kernel inthis instance refers to a sub-array pattern that is repeated throughoutthe array in a similar or different pattern). The arrangement of FIG. 7Bis useful, for example, in providing multiple imaging systems on acommon array substrate 174. FIG. 7C shows an array of lenslets 176 thatare irregularly spaced from each other in unique or semi-unique formalong the array surface 178. Note that FIG. 7C also illustrates thatlenslets can have varying shapes, according to the invention, such ascircular, hexagonal, square, triangular, trapezoidal, and rectangular.As above, the interstitial spacing 180 between lenslets 176 are opaquelycovered or stopped via optical techniques, so as to reduce or eliminateradiation transfer through the regions 180. Note also that the shape ofthe array substrates are a matter of design choice, such as circular asin the substrate 166, 174 of FIGS. 7A and 7B, and rectangular as in thesubstrate 178 of FIG. 7C, so as to fit with a selected opto-mechanicalassembly or system. FIG. 7D illustrates an array of lenslets 182 thatare arranged in a radial fashion; while FIG. 7E illustrates lenslets 184that are arranged with varying distances from the center 186 of thearray 188. The configuration of FIG. 7E is one used often, in accordwith the invention, to achieve selected magnification in an image,similar to the technique shown in FIG. 1, so that a given channel canspread outwards relative to the optical axis. Note in FIG. 1 that whilethe lenslets 56 extend in varying distances from the axis 26, thepattern need not be radial such as shown in FIG. 7E.

Those skilled in the art should appreciate that the lenslet sizes, andthe number of lenslets, within the arrays of FIGS. 7A-7E are shown forillustrative purposes and are not to scale. In reality, the lenslets ofthese figures are much smaller as compared to the substrate size; andthere are typically many thousands of lenslets within a given array.

FIG. 8 illustrates a stack 190 with microlenslets 191 arranged in atilted manner, relative to the optical axis 192 between the object 194and the image 196, so as to achieve selected demagnification. The effectis similar to FIG. 1 except that the lenslets 191 themselves are tiltedrelative to the axis 192; while the channels. 200 are substantiallyparallel to the axis 192. This tilting of lenslets inwards and outwardsprovides for selected magnification of the stack 190. However, problemsassociated with tilting lenslets as in FIG. 8A include fabrication andprocess limitations. Diffractive steering lenslets generally operatebetter. Nevertheless, diffractive surfaces can be micromachined (orprocessed) so as to "blaze" the overall array surface so as to producemacroscopic Fresnel-like surface kineforms and to provide tiltedsubstrate regions prior to lenslet formation. This facilitates thetilting of lenslets as in FIG. 8A. Note also that tilted lenslets andsloped lenslet channels can be combined together in a stack to achieveother varying effects such as magnification.

In an alternative configuration, and as shown in FIG. 8A, a stack 202can provide selected magnification by utilizing lenslets 204 withdiffering optical powers: the inner lenslets 204a of the stack 202,i.e., those lenslets closer to the optical axis 206, have a loweroptical power as compared to the lenslets 204b which are further fromthe optical axis 206. Additionally, diffractive lenslets can be used toenhance this effect. Note, however, that the main issue addressed withvarying optical powers and aperture sizes (including apodization,described herein), is aberration control; while luminance variations(created, for example, by cosine 4 losses) are addressed by tilting asin FIG. 8A. Accordingly, by changing lenslet power, aperture sizes,apodization, and other parameters discussed herein, optical efficiencycan be compensated and corrected as a function of the distance from theoptical axis to the edge of the respective arrays.

FIG. 9 shows a sequence 210 of stacks 212 arranged along an optical axis214 so as to provide an erect image 216 of the object 218. Asillustrated, the stack 212a has two arrays of refractive lensletsdisposed therewith (shown illustratively as two lenslets 220); whilestack 212b has an array of non-refractive lenslets (shown illustrativelyas a single lenslet 222). This design provides an internal, invertedimage 223 of the object 218 within the first stack 212a so that thefinal image 216 is erect. Generally, therefore, 2n+1 internal images arerequired to generate an erect image, where n is an integer 0,1,2,3, . .. . FIG. 9 also shows in internal stop 224 arranged within the stack212a so as to limit the field of view and to restrict the transfer ofunwanted radiation (e.g., scattered radiation) to the image 216, therebyboosting MTF. The stop 224 can, for example, be micromachined internalto the stack 212a, electro-formed or inserted as a separate element.

Similar to FIG. 9, FIG. 9A shows a sequence of stacks 210' arrangedalong an axis 214' to provide an inverted image 216' of the object 218'.In this configuration, the refractive elements 220' do not generate aninternal image; and hence the final image is inverted. Generally, 2ninternal images within a sequence of stacks will provide a non-erectimage, where n is an integer 0,1,2, . . . . Note that if the stacks donot generate a continuous and erect image, the resulting image216a'-216c' is jumbled relative to its original appearance since eachchannel images and inverts a separate FOV, shown illustratively by thedotted sections 218a'-218c' (such as the internal image 223 of FIG. 9).

As discussed above, microlenslet surface structures can take on manyforms, including: (a) refractive optical elements, (b) diffractivekineforms, (c) high order, high efficiency diffractive steering orfocusing lenslets, (d) holograms or holographic lenslets, (e) computergenerated holograms, (f) effective index modulating surface arrays, (g)apodizing or other spatial filters, or (h) other features typicallygenerated by lithographic and semiconductor fabrication technology.FIGS. 10-14 illustrate exemplary microlenslets and optical effectscreated by certain of these lenlset forms.

In particular, FIGS. 10A-10C illustrate, respectively, the constructionof a holographic lenslet array, a resulting holographic lenslet, and theoverall holographic array lenslet operation. In FIG. 10A, a content beam230 and a reference beam 232 (both typically electromagnetic lasersources such as known to those skilled in the art of holography)interfere within a substrate 234 which reacts (such as with emulsion) toform holographic lenslets 236 (shown illustratively as an interferencepattern), FIG. 10B. In operation, FIG. 10C, an object 238 whichgenerates a light beam 240 that interacts with the lenslet is "steered"off at the sensitivity angle θ.

FIGS. 11A and 11B illustrate, respectively, construction of phasemodulation lenslets and the overall operation of phase modulationlenslets. In FIG. 11A, a substrate 242 is modified with phase-changingradiation or deposition 244 so that the phase angle φ of the incidentelectromagnetic field, E, is transformed to E* by an amount such asninety degrees, FIG. 11B.

FIG. 12A illustrates the manufacture of an index modulating lenslet byion implantation or exchange. In the illustrated example, the radiation246 incident on the radiation sensitive substrate 248 is in the form ofa Gaussian beam so as to effect either a gradient index lenslet 250,FIG. 12B, or a Gaussian-shaped index modulation lenslet 252, FIG. 12C(note that the shape of lenslet 252 is easily modified to another formby changing the shape of the input beam, e.g., to a Bessel irradianceprofile). In an alternative index modulating lenslet configuration, FIG.12D shows a substrate 254 that incorporates a series of nanometer widecuts 256 that are much smaller than the wavelength of operation. Thesecuts operate to decrease the density of the substrate and to reduce theeffective optical index (i.e., air is about 1.0).

Lenslets according to the invention are preferably made withlithographic processes. By way of example, a sequence of photomasks aregenerated with features that correspond to the desired lensletdimensions. The substrates are then coated with photoresist. Using aphotomask, the resist is then exposed to the sensitizing radiation(typically ultraviolet, electron, or x-ray) followed by curing. Thecured and uncured resist are then coated with a metal or other maskingmaterial; and the uncured polymer and metal coatings are removed toexpose regions of bare substrate. The exposed areas of substrate arethen etched using plasma, wet chemical, reactive ions, or othertechniques to create a relief pattern. This process is thereafterrepeated for successive photomasks to generate a three-dimensionalrelief structure corresponding to the desired refractive or diffractivelenslet.

The making of a negative mold for use in polymer or sol gel molding orreplication further illustrates useful lithographic processes in accordwith the invention. By way of example, and with reference to FIGS. 13Aand 13B, negative lenslet features are first molded into a metal mastermold 260; and this mold is used to form a substrate 262 with integrallenslets 264 by conventional processes, e.g., injection molding, diepressing, and stamping, known to those skilled in the art. Certainreplication techniques, according to the invention, utilize a negativemold as above, and without heating. The mold 260 is coated with arelease agent, and followed by the lenslet material 262 in the form ofan epoxy, polymer or sol gel. The lenslets features are transferred to abulk substrate, such as a glass plate, using an adhesive, thermoset orother bonding agent. With reference to FIG. 13B, the flat side 262a, forexample, is bonded to such a substrate.

FIGS. 14A and 14B illustrate arrays of lenslets 270 formed bydiffractive kineforms. FIG. 15A shows a diffractive beam steeringlenslet array 272 that redirects a wavefront 274 (of the wavelengthcorresponding to the microfeatures in the lenslet array 172) at an angleθ (note that such an array can also be a focusing lenslet array). FIG.15B similarly shows a holographic array of lenslets 276 (or phase orindex modulating array) disposed into a substrate 278 to effect beamsteering of an incoming wavefront 280. A computer generated hologramlenslet array 282 within a substrate 284 provides similar effect toprovide focusing of an incident wavefront 286, such as shown in FIG.15C.

FIG. 15D illustrates an array of gradient index (GRIN) lenslets 288formed by ion implantation, back fill with polymer or gel, or ionexchange as in conventional GRIN elements. FIG. 15E shows an apodizationfilter 290 that has a selected transmission function (e.g., Gaussian oranti-Gaussian) and used in conjunction with a kineform lenslet array 292to effect certain desired transfer characteristics, such as uniformityof illuminance (e.g., cosine-to-the-fourth losses, and modification ofGaussian laser beams). FIG. 15F shows a refractive lenslet array 294formed in conjunction with an array of stops 296 to effectcharacteristics such as FOV and luminance uniformity. Within a givenarray, the stops 296 can include apertures of different diameters so asto (a) be consistent with the lenslet channel diameter or so as to (b)balance illuminance uniformity from the center to the edge of the array.The effect of (b) occurs because lenslets in the center of the arraywill transmit at greater efficiency as compared to lenslets at the edgeof the array unless the lenslet channels at the edge are a differentlens configuration or have larger clear apertures. Lenslets can also beformed through lithographic deposition of material for refraction orphase modulation (or retardation), such as shown by the lenslets 298deposited onto the substrate 300, FIG. 15G.

FIGS. 16A-16E illustrate the impact of lenslet FOV on imagingcharacteristics. The FOV becomes a practical design and fabricationissue due to the relationship between lenslet SAG and curvature giventhe state-of-the-art fabrication capabilities (that is, the FOV iseffectively limited in lenslets with high power--typically smalllenslets--since the image at wide field angles is blurred andpractically non-existent). If the SAG is less than curvature, thenlenslets are, generally, easier to fabricate. In FIG. 16A, an array oflenslets 302 are arranged adjacent to a RGB (red, green, blue) pixelatedobject 304 such as a color matrix display. In FIG. 16A, the lensletclear apertures are clearly smaller than the pixelated objectdimensions. In FIG. 16B, on the other hand, the lenslet clear apertures306 are approximately equal to the RGB pixelated dimensions; and in FIG.16C, the lenslet dear aperture 308 is greater than the pixelated objectdimensions.

FIG. 17A illustrates an array of lenslets 310 where each of the lensletshas an equal, though non-overlapping FOV 312. Note that in such a case,where little or no FOV overlap occurs, a defective lenslet 310 wouldresult in losing some of the image. However, in the case of FOV overlap314, such as shown in FIG. 17B, the loss of a single lenslet throughdefect has a lesser impact on overall image quality since adjacentlenslets 316 transmit some--or all--of the image covered by thedefective lenslet.

Stacks constructed according to the invention generally include, atleast, four lenslet array surfaces formed with at least two substrateelements. Assembly can include discrete air-spaced elements withexternal mechanical fixturing and/or mechanical spacers placed betweenthe elements and arrays. Such a stack provides a stable, monolithicstructure which easily integrates into a system, device or product. Withreference to FIG. 18, a monolithic stack 320 is shown to illustrate thefunction of fiducial marks, spacers, and interstitial lensletmicroalignment features. The stack 320 includes four arrays ofrefractive lenslets 322 disposed with two substrates 324, and two arraysof diffractive lenslets 326 (diffractive kineform type) disposed withtwo substrates 328, one of which is drilled and pinned with assemblypins 330 to a mechanical mount 332. Fiducial marks 334 are used tocoalign the arrays of lenslets 322, 326 to provide for efficient imagingof the object 336 to the image plane 338. The stack 320 additionally hasspacers 340 disposed within the stack so as to provide for propercoregistration and spacing between arrays. The spacers 340 can also bedrilled and pinned, such as shown as pin 340a, to a substrate. Note thatcoalignment and spacing between arrays can also be made directly fromthe substrate material, as shown by spacing element 342, or by the maskmaterial 344 arranged at interstitial locations between lenslets 322,such as shown by spacing element 346.

FIG. 19 illustrates a Hartman Transform Encoder 350 constructedaccording to the invention. The encoder 350 divides the opticalwavefront (or object space) into discrete parts for individual imagingand analysis. That is, it takes a continuous image 352 and breaks itinto a set of discrete pixels 354, each of which is independentlyevaluated. Accordingly, the SAM 350 (including two non-refractivelenslet arrays 350a and two refractive lenslet arrays 350b) of FIG. 19images a checkerboard object 352 into a corresponding image 354 whichcan be conveniently coincident with a photodiode array 356 (here shownby a dotted outline, including detector pixels 356a), and associatedelectronics 358, so as to process individual image signals separately.

As discussed earlier, multi-element SAMs of the invention with one ormore intermediate image planes facilitate the insertion of passive oractive media at a field image or at a collimated space between twolenslets in the stack. Active media located at the field stop provides aconvenient forum from which to accomplish optical processing. Consider,for example, FIG. 20, which represents one channel 370 of a stack andwhich includes an intermediate image 372. The channel 370 furtherincludes a light modifying element 374. By way of example, the elementcan be a pupil with a selected transmission function, which in linearsystems theory provides a canonical processor: the output transformfield is the convolution of the corresponding input with the Fourierinverse of the pupil's transfer function. However, the element 374 canalso be an electro-optic modulator, a liquid crystal light valve, anactive color filter mosaic, a spatial light modulator, a computergenerated hologram, and even gain media to accommodate a wide variety ofapplications for optical transform systems, compact optical correlators,optical network and computing systems, switching systems and numerousother optical signal processors. Fixed passive spatial filters, colorfilters, or encryption filters can also be co-located at the image 372in the stack assembly to create a wide variety of fixed or passiveoptical signal processing systems. The inclusion of such devices at theinternal image provides optical processing of each of the channels, ifdesired, in a massively paralleled processor.

FIG. 21 shows a scene generation apparatus 380 constructed according tothe invention. A computer 382 is used to generate a display pattern on aFPD 384 such as the computer display. A tiled stack 386, shown in aperspective view, thereafter images the display 384 as a large formatdisplay 388 suitable for a number of uses (note for clarity ofillustration that the computer and display are shown parallel to theoptical axis 390 while in fact it would be perpendicular to the axis 390to enable reimaging). By way of example, the apparatus of FIG. 21 issuitable to provide an inexpensive, compact wide FOV display screen 388.

FIG. 22 shows a side view of a digital camera constructed according tothe invention. Briefly, the camera body 392 and optics 394 areconstructed by known methods to generate a 35 mm film-formatted imageplane 396 (shown by a dotted line internal to the body). In accord withthe invention, a stack 398 is configured to fit with the body 392(depending upon the camera body configuration 392, the stack 398 isinternal or external to the body and connected by appropriate mechanicalfixturing (not shown)) so as to reimage the image plane 396 onto a solidstate device 400, e.g., a CCD. In order to achieve this, the stack 398magnifies or degmagnifies the image 396 selectively so as to fit thepixelated dimensions of the device 400. In this manner, the scene "X" asviewed by the camera 392/394 is conveniently converted to electricalform for display on a device such as a computer 402.

FIG. 23 shows a four-element stacked lens array imaging system (SAM) 500of the invention. The SAM 500 includes a hybrid assembly (i.e., "stack")of lenslet arrays 502, with precise registration among the plurality ofindividual lenslet optical channels 504 defined by the arrays 502. Thisallows for optical image transfer from object space 506 to image space508. The stack 500 assembly of lenslet arrays 502 may perform eithermagnification or demagnification, depending upon specific applications.

More particularly, FIG. 23 illustrates a stack having four elements orsubstrates 510. In a preferred embodiment, all substrates are silica.Each substrate is illustratively shown with a constant thickness ofabout 400 microns, though other thicknesses are possible and envisioned.By way of example, the diffractive element substrates 510a may have athickness of 1.0 mm while the refractive element substrates 510b mayhave a thickness of 300 microns. The stack has a total of two arrays502a of diffractive lenslets 505a and four arrays 502b refractivelenslets 505b, although this number is purely exemplary. For example, ina large screen display, the stack could comprise three diffractivemicrolens arrays and three refractive microlens arrays. Regardless, eachrefractive array has integral inter-element stops 512, such as chromebaffles, in open areas (i.e., interstitial regions) between lensletchannels 504 to form entrance and exit pupils, field stop and bafflesfor stray light rejection and control of crosstalk. The design of themagnifying microlens array stack 500 utilizes arrays of tilted, off-axisoptical channels 504 with respect to the central optical axis betweenthe image 508 and object 506.

The left surface of the first element 510a1 has a planar surface 511 andis adjacent to the object plane 506. The right surface 514 of the firstelement 510a1 has diffractive lenslets 505a1 that function as asphericcorrectors that correct for residual aberration. Both monochromaticaberration and chromatic aberration correction is addressed usingdiffractive lenslets that provide negative dispersion and which requirevery little paraxial power to correct for chromatic aberrations.

The middle two elements 510b1, 510b2 in the stack 500 of FIG. 23 haverefractive lenslets 505b on each array surface 502b. An inverted fieldimage 515 is formed between the second and third elements. The fourthelement substrate 510a2 has a left surface 510a' with a diffractivelenslets 505a2 for purposes similar to the first element 510a1. Theright surface 516 of the fourth element 510a2 is planar and is adjacentto the image plane 508. The four elements 510 of the stack may be directcontacted and cemented in place.

The stack of FIG. 23 interlaces the images from each optical channel(defined by sequential lenslets in the arrays) to create the final totaluniform image 508. If every channel 504 was parallel, the demagnifiedimage from one channel 504 would not overlap the image from itsneighboring channel. In that case, there would be a demagnified imagepatch corresponding to each channel surrounded by either a region of nolight or a mis-interlaced blur. Thus, the lenslets 505 in the array 502which are nearest to the image 508 have a higher packing density thanthe others. This `off-axis" type of design not only allows theindividual channels 504 to have demagnification, but it also allows thearray of optical channels to converge towards the final demagnifiedimage. From FIG. 23, it can be seen that the refractive and diffractivelenslet arrays 502 form channels 504 from object to image space thatbend inward toward the central optic axis.

In a preferred embodiment, the first and last refractive surfaces (leftto right) have identical surface figures, while the second and thirdrefractive surfaces (left to right) also have identical surface figures.The lenslet packing configuration is circular apertures on a squareCartesian coordinate array. The clear aperture for the object side isillustratively 10 mm by 10 mm. The overall area for each substrate isillustratively 12.5 mm by 12.5 mm. Overall, the stack 500 illustrativelyprovides for a 60 by 60 array of optical channels 504. FIG. 23 alsoillustrates the effect of increasing axial tilt of each optical channelpath to converge on the image plane.

To simplify fabrication of mask tooling as well as the lenslet arrays,the refractive lenslets (and similarly the diffractive lenslets) withina given array are identical made and uniformly spaced, although this ispurely exemplary. By example, the first refractive array 502b1 haslenslets 505b with a diameter of 150 μm and a lens spacing of 161.5 μm.The second refractive array 510b2 has lenslets 505b with a diameter of120 μm and a lenslet spacing of 158.5 μm. The third refractive array502b3 has lenslets 505b with a diameter of 120 μm and a lenslet spacingof 157.6 μm. The fourth refractive array 502b4 has lenslets 505b with adiameter of 100 μm and a lenslet spacing of 155.8 μm.

In the alternative, the surface of each lenslet array may containrefractive and/or diffractive kineforms, high order, high efficiencydiffractive steering or focusing lenslets, holograms, effective indexmodulating surface arrays, apodizing or other spatial filters, or otherfeatures typically generated by lithographic and semiconductor-typefabrication technology. One or more macroscopic planar or refractivelens surfaces may be incorporated in addition to the lenslet arraysurfaces. Each element in the stack may be of a finite thickness havingtwo surfaces, wherein each surface may have the various characteristicsdescribed herein. One surface is typically the input surface for thatelement, wherein the other surface is typically the output surface forthat element.

As used herein, the term `hybrid" sometimes refers to a combination ofthese different types of optical surfaces (e.g., diffractive,refractive, etc.) for the lenslets in each array. Hybridization providesexcellent color aberration or other correction for high efficiency, highmodulation transfer function and uniformity over a large apertureoptical system.

The input and/or output surface of each array provides a clear aperturesystem with performance at least equivalent to, or greater than, themechanical aperture of the device. This allows for seamless tiling ofthe stack optics into an infinitely scaleable, tiled, massive parallelprocessed array for a very large scale image display or imageacquisition over a large field of view. Microelectronics-typefabrication of tiled structures allows for cost-effective manufacturingof large scale assemblies. For example, a single photomask may be usedin conventional microlithography and VLSI manufacturing processes togenerate the diffractive and refractive lenslet arrays. Massive parallelprocessing of discrete tile subassemblies allows for cost effectivecomputer control of large scale, seamless tile array systems at veryhigh speeds for real-time video rate (or faster) processing.

The system 500 reimages a discrete pixelated object space 506 into adiscrete array image space, or reimages a continuous object 506 into acontinuous image 508, without dark spaces, gaps or blurred regionsbetween pixels or local image areas at the image plane. This isaccomplished by careful image interlacing of adjacent channels 504 orkernels of channels in the stacked array structure.

Image interlacing of adjacent microlens channels 504 provides a uniform,high efficiency optical tile system with a total optical path length orworking distance which scales with size and f-number of the lensletchannels 504. The system 500 therefore provides for a flat panel opticalsystem with a thickness, weight and mass that is much smaller than aconventional macroscopic lens or mirror optical system.

The microlens array element surfaces may consist of a uniform array oflenslets of equal surface figure at regular spacing, or kernels ofsubarray lenslets of equal surface figure at regular spacing, oruniquely different lenslets at regular, irregular or changing spacingdepending upon the location from the mechanical center of the surface.

The individual lenslet apertures may be round, square, hexagonal orother shape. Also, the apertures may be equal to or smaller than thelenslet-to-lenslet center spacing, to leave a non-lensed zone betweenlenslets.

Either the lenslets 505, lenslet surfaces and/or inter-lenslet spacing(here shown as items 512) may contain hard stops, baffles, masks oropaque zones for control of crosstalk, elimination of stray light,reduction of aberrations, maximization of image contrast, andoptimization of modulation transfer function. Intra-element stops 512 oropaque zones may be fabricated by chemical modification of elementstops, or opaque zones may be fabricated by chemical modification ofelement substrate material, trench etching and backfill with opaquematerials, thermal or other physical processing. Surface stops may befabricated using physical deposition, chemical modification, printing orother processes for depositing or locating opaque materials ininterstices between lenslets. Inter-element stops 512 or baffles mayconsist of metal (e.g., chrome) or other opaque masks which can alsoprovide for accurate spacing and precision location of adjacent lensletsin the array.

The design of the stack for stray light control considers four sourcesof undesirable light. First, it is desirable to block light from theregions between optical channels. Second, it is desirable to eliminateor at least restrict the possibility for light to cross through multipleoptical paths and to exit the system at other than designated channels.Third, an antireflection coating is preferably included to eliminatestray light from multiple surface reflections. Fourth, the opticalsurfaces should have minimal scattering.

The third and fourth sources of stray light are addressable uponfabrication of the optics. The first and second sources of stray lightrequire the design of efficient baffles and hard stops between thelenslets. The source of stray light from regions between the opticalchannels is restricted by coating the surfaces between lenslets with anopaque coating. The second source of stray light is reduced oreliminated by additional baffling or by encapsulating each opticalchannel in an opaque cylindrical baffle 521.

One method by which the system 500 accomplishes magnification ordemagnification is by outward or inward tilting of selected lensletoptical channels 504. The system 500 may also utilize lenslet arraychannels to effect magnification or demagnification by outward or inwardtilting of channel optical axes. Magnification or demagnification can bedivided equally or unequally among elements 510 of the stack. In apreferred embodiment of the stack of FIG. 23, the amplitude ofmagnification or demagnification is divided equally about the fieldimage 515 between the first and second elements, and the third andfourth elements (left to right).

Individual lenslet sizes may be smaller, equal to, or larger than theobject or image space pixel dimension. Larger lenslets 505 willencompass fields of view over many pixels in object or image space, or afield which exceeds the aperture of the lenslet with potential overlapamong the fields of view of multiple lenslet channels. Lenslets of equalaperture size to field of view in object space 506 may transfer theimage of many or just one pixel or field of view equal to the lensletaperture. Lenslets 505 of smaller aperture size may utilize or interlacethe images of many lenslets to image one point in object space to apoint in image space.

Lenslets which have an aperture size equal to field of view is the leastpreferred configuration due to the extremely tight tolerance required infabrication, registration and low defect density needed for gooduniformity of image transfer. Designs with the larger lenslet aperturesrequire simpler masks for fabrication with fewer features; but very lowdefect density can be tolerated unless multiple lenslet channels areused to image a single point in object space. On the other hand, morecomplicated masks for fabrication are required for lowest packingfraction for optical efficiency, but allow for the greatest tolerance inregistration and defect density due to the interlacing of images frommany channels to image a point in object space into image space.

In one embodiment, approximately five channels transmit lightsimultaneously from each point in object space to image space. That is,a single point in object space radiates into five adjacent channels in asquare pack geometry. Thus, if a lenslet channel has a defect, theinformation in object space is not lost. Instead, it is transformed bysurrounding lenslet channels, but with a fractional loss of intensity.In one embodiment, the resulting field of view for a lenslet in objectspace is 11.86 degrees or 168 μm. This imaging of a single point sourceof light through more than one optical channel increases opticalthroughput, achieves appropriate image interlacing and maximizes imagingreliability. The illustrated f-number of each lenslet channel 504 atdesign conjugates is f/6.33, while the resulting effective f-number ofthe stack is approximately f/3.9. Note that a hexagonal close packedarrangement of lenslet arrays could reduce the effective f-numberfurther.

The system can provide either inverted or erect-images at the imageplane 508 output. Systems with erect images require an odd number (1, 3,5, . . . or 2n+1, where n is an integer number) of field stops orintermediate field image surfaces internal to the stack structure. Thesimplest configuration has one intermediate image plane 515 where afield stop or field lenslet can be positioned. Systems with invertedimage output have zero or an even number of field stops or field imagesurfaces internal to the stack structure.

Systems with internal field images may incorporate field stops in theform of micro-machined, electroformed, molded or other aperture platesfor aberration control, improvement of image quality or modulationtransfer function.

Generally, the minimum requirement contemplated for the imaging systemof this embodiment is four array surfaces and two elements. The stack ofelements can be assembled as discrete, air-spaced elements with externalmechanical fixturing or an internal mechanical spacer. Assembly using aninternal mechanical spacer can provide for a stable, monolithicstructure for easy integration into a system or product.

The element surfaces and/or spacers may include fiducial marks tofacilitate micron-level registration and location of components. Thesefiducial marks can be deposited, or male or female patterns can beetched into surfaces at interstices between microlens elements. Theopposing surface of the next element, or the spacer between elements,can also have fiducial marks or mating surface relief patterns tofacilitate assembly or co-location of elements and components of thestack assembly. Otherwise, the lenslet apertures can register into oneor more mask plates between adjacent elements of the stack to providefor co-location and precise positioning in x-, y- and z-axes of thestack assembly.

Monolithic, self-alignment construction of stack assemblies allows forcompact, high-performance optical systems with superior structural andenvironmental integrity, in comparison to conventional optical systems.The system optics can be assembled with buried and cemented surfaces foradded reliability and impermeability to contamination or dirt.

An intermediate image plane affords the opportunity to design in passiveor active media at a field image or collimated space between two arraysin the stack. Optical wavefronts or images can thus be demagnifiedequally or nonu-niformly between input array(s) to the field space andoutput array(s) to the object space, Active media such as electro-opticmodulators, liquid crystal light valves, active color filter mosaics,other spatial light modulators, computer generated holograms, non-linearoptical or linear optical, and even gain media, co-located at a fieldstop accommodate a wide variety of applications for optical transformsystems, compact optical correlators, optical network and computingsystems, switching systems, and numerous other optical signalprocessors. Fixed passive spatial filters, color filters, or encryptionfilters can also be co-located at a field image in the stack assembly tocreate a wide variety of fixed or passive optical signal processingsystems. The compact, monolithic nature of the stack assembly allows forease of assembly and integration with internal devices plus associatedelectronics and mechanical fixturing in many applications.

The stack components and assemblies of FIG. 23 may be fabricated using awide variety of materials and methods compatible with volumemicroelectronics assembly, tooling and equipment. Substrates 510 can besemiconductor, glass, single crystal, polycrystalline, liquid crystal,polymer or other optically transmissive material amenable to processinginto microlens arrays. In a preferred embodiment, the hybriddiffractive/refractive optics are fabricated in optical grade polymerusing precision replication and molding techniques for minimumthickness, low weight and low cost. Metal or other solid negativemasters can be used for mold fabrication of array elements and stacks.Array elements can be cemented to bury surfaces for added reliability.Spacers between elements can be glass, metal, polymer, crystalline orother appropriate structural or optically opaque medium to allow forregistration, and for other optical and mechanical properties. Activeand passive devices located between elements, particularly at fieldimage planes, may incorporate electronics and mechanics for assembly andfixturing of system products.

The system technology can apply to applications across the opticalspectrum, from deep ultraviolet to the far infrared. Indeed, manysemiconductor materials with ease of processing using microelectronicsfabrication technology have excellent infrared transmission propertiesfor novel infrared applications. The compact, flat panel nature of thesystem of the present invention allows for easy integration with animage plane device such as a focal plane array detector. The systemoptics can also function as an optical signal processing window thatisolates and protects the focal plane array device in a controlledenvironment atmosphere such as cryogenic or other thermally-controlledenvironment (e.g., heated, isothermal, non-cryogenicically cooled). Inaddition to environmental protection, use of an active attenuator orfilter can afford protection from intense light or unwanted spectralcomponents.

The system optics of FIG. 23 thus provide a singular optical assembly inimaging, display or detection applications using a single flat paneldisplay, focal plane array, or other direct display device or detectordevice. The ability to fabricate system optics with zero edge or clearaperture to the mechanical edge of the output or input surface allowsfor infinitely scaleable tiling of massive parallel processed arrays forvery large flat panel displays or very wide area, high resolution imageacquisition systems.

Referring now to FIG. 24 (which is a subcomponent to the systemembodiment of FIG. 25), there illustrated is an embodiment of theoptical imaging system 520 of the present invention operable in amagnification mode. The system 520 is used to reimage and magnify thepixelated object display 522 from a miniature FPD to a larger imageplane 524. Such miniature electronic displays exploit microelectronicsmanufacturing technology to produce high resolution, active matrixdisplays at high yields and low costs. Then, assembly of the hybriddiffractive/refractive microlens array magnifier to a miniature FPDeffects a large visible field 525 with a high fill factor in a lowweight, low profile, high performance package. The result is a viable,scaleable process for economical fabrication of large size passive oractive matrix flat panel electronic displays with high efficiency, highresolution and high contrast, but with low profile and low weight fornumerous military and commercial applications.

FIG. 24 also shows seven lenslet arrays 526 on four substrates 528, andan array of stops configured on a common aperture plate 530. The arrays526 include either refractive lenslets 532 or diffractive lenslets 534.

The stack 520 of FIG. 24 is easily integrated into a system such asshown in FIG. 25. As seen in FIG. 25, the output screen 550 of system549 can be a plurality of tiles 552 that provide the resultingultra-large flat panel display. Such a display 550 finds commoninformational display usage in sports stadium and arena scoreboards,high definition television, outdoor advertising, airport runways,entertainment and gaming, virtual environments, virtual conferences,conventions, and countless other areas. The display 550 is a largescreen, computer driven, adaptive, active matrix flat panel display withhigh uniformity of luminance over a wide field angle. The process oftiling a matrix of repetitive stack elements, e.g., a stack 520 of FIG.24, is thus an extremely powerful concept for creating large scaleimages in a cost effective and reliable manner.

The display 550 has utility in areas and markets where well-known andrelatively old projection displays will not work or are not appropriate,such as within harsh environments. In extreme environments, a largemonolithic FPD 554 often fails, or the image is distorted, due to theextreme temperature range that the FPD 554 is typically exposed to. Incontrast, the imaging system 549 isolates and insulates the FPD 554 fromthe environment. Its structure allows the opportunity to build in acompact heater/cooler to maintain uniformity of FPD performance for allambient conditions.

As another example, conventional avionics displays often suffer from lowcontrast in direct sunlight. However, the imaging system of the presentinvention provides a narrower direct field of view to the pilot. Thetransreflectance surface of the optics reflects and diffuses sunlightfor high contrast. The optics of the imaging system also provides forhigh brightness and contrast at all practical ambient light conditions.

With regard to very large electronic message displays like those used insports stadiums and arenas, these displays suffer from inherent highcost, poor performance, excessive weight and structural problems,enormous power consumption, poor reliability and difficulty and largemaintenance expense. In contrast, the ultra-large, high resolutiondisplay 550 of the FIG. 25 embodiment provides for a seamless, scaleabletile construction. It has all-weather outdoor and indoor direct viewcapability with a variety of virtual and adaptive screen features.

FIG. 25 also shows a computer 556 coupled to FPD boards 558a-d, whichserve to drive each of the respective FPDs 554 in the tile.

With further reference to FIG. 24, the first element 528a in the stackhas a left surface 529 that comprises an array of refractive lenslets532 that receive light from the miniature FPD 522. The FPD may be acolor array comprising light sources of the three primary colors toachieve a polychromatic display. Color displays are achieved using akernel format of discrete red, green and blue pixels in a matrix arrayformat in which the colors are repetitively interleaved by alternatingrows or columns of a discrete color. The discrete pixel nature of FPDsallows for independent address of individual pixels or multiplexedkernels of pixels. The discrete pixel structure and electronic addresscapability of FPDs to create images are appropriate for microlens arrayswith discrete lenses precisely registered to discrete FPD pixels.Further, the limited wavelength bandwidth of monochrome or polychromeFPD pixels has the advantage of placing limited wavelength dispersioncorrection constraints on the design of individual lenslets in thearrays. It also allows for blaze angle optimization of diffractionefficiency for optical transfer from the input FPD image plane 522(i.e., the object plane of the lenslet) to the output image plane of thelenslet array.

Furthermore, the microelectronic fabrication of the FPD array structureaccording to the invention provides for reliable registration andaperture definition of FPD pixels, and provides fiducial registrationmarks for alignment of individual lenslets and the overall lenslet arrayto the FPD pixel array.

The refractive optics of the left surface of the first element 528aisolate and collimate the light from the FPD 522, and presents the lightto the right surface of the second element 528b, which comprises anarray of diffractive microlenslets 534. The first element 528a achievesspatial control of the optical emission from the FPD 522 and provides anintermediate image plane (not shown) which can be more effectivelytransformed by the second element 528b in the stack. The intermediateimage plane is needed because oftentimes miniature FPDs have uniqueoptical characteristics that are not necessarily well-suited forefficient optical transfer by a lenslet array.

Although not shown, an aperture plate could be placed to the left of thefirst surface of the first element 528a, possibly located at the Talbotplane of the FPD 522, to define and isolate individual FPD pixels forthe left refractive surface of the first element. The two array surfacesof the first element 528a correct for the color bandpass of theassociated pixel, and transform the FPD object plane 522 into infiniteconjugates for efficient optical processing by the second element 528bin the stack.

The second element 528b in the stack is a diffractive microlens 534array at the right surface, with a planar left surface 527. The lensletarray comprises a plurality of sequential diffractive optical elements534 that provide for two dimensional successive incremental angulardisplacement ("fanout") and, therefore, magnification of the collimatedlight 529. In a preferred embodiment, the element 528b may achieve fouror five times magnification. The fanout grating array is blazed for theappropriate color. The exact incremental angle of the sequential fanoutmay be between three and fifteen arc-minutes to effect a five times orgreater magnification with an aspect ratio of less than one to one.

The third element 528c in the stack has a diffractive lenslet array 534on its left surface, and a refractive microlens array 532 on its rightsurface. The third element 528c spatially redirects (i.e.,re-collimates) the now-expanded light emanating from the second element528b to near 100% fill factor.

The fourth and final element 528d in the stack has a refractive lensletarray 532 on its left surface, and a diffractive microlens array 534 onits right surface. The fourth element 528d serves as the output lensarray and may be designed to limit the output field of view, or toeffect trans-reflectance optics or other optical transform for contrastenhancement. For example, the fourth element 528d may utilize anadditional fanout grating for efficiently modifying the angular field ofview for specific angle or wide angle viewing.

Each element 528 in the stack may incorporate fiducial registrationmarks for precise and accurate tolerancing or the overall assembly, aswell as registration of the stack to the FPD 522. For example, if thestack is fabricated as a registered stack of air-spaced refractive anddiffractive arrays, each stack layer or element is provided withfiducial registration marks to aid in alignment. Simple black nylon oranodized aluminum spacers may be used for precise dimensioning of theair gap of the stack layers. It may also be possible to incorporateetched relief areas and/or thru-holes to aid in registration.

In operation, the optical imaging and magnifying system of FIGS. 24 and25 refracts and diffracts the light from each uniformly spaced pixel inthe smaller source array of the FPD. It does so at specifically designedvarying angles from the normal to produce a larger tile of discretesampled array, but with constant magnification, contrast and luminanceacross the surface.

The imaging system of the invention need not be monolithic inconstruction, but may instead consist of a hybrid stack of opticalarrays appropriately registered to each other in the form of a stackedarray magnifier (SAM).

Further, to control stray light and enhance contrast, a spatial filteror image transfer array may be utilized between the solid state emitterarray 522 (i.e., the FPD or LCD) and the magnifier array. Also, it isnot necessary that the output display side optics 524 of the system havea 100% fill factor. However, a 100% fill factor to the edge of theoutput plane provides for seamless tiling of SAM-coupled FPDs to effectscaleable, large format displays limited in size only by the parallelprocessing computing capability for control and synchronization of thetile elements.

It is also not necessary that the stack's pixel format have a squareappearance. The output display side 524 of the system is not restrictedfrom including a technical screen or optical array for purposes ofenhanced uniformity and field of view.

Referring now to FIGS. 26 and 27, there illustrated is the opticalimaging stack 570, FIG. 26, which is used in a large area, flat panel,X-ray reimager system 580, FIG. 27. In this embodiment, the system 570is functioning as a demagnifier. Prior art systems suffer from highcost, poor performance, excessive weight and structural problems, alongwith slow response, high power consumption, poor reliability anddifficulty and high cost to maintain.

In contrast, the system 580 provides for a seamless, scaleable tileconstruction with a discrete, low cost CCD readouts 582 integrated by aparallel process computers 584. The system 580 of this embodiment is notlimited to usage with an X-ray input 586; instead, this embodiment hasapplications in image intensifiers, very wide field of view and wideazimuth elevation fire control and surveillance systems, diagnosticimaging systems for non-destructive testing and medical applicationssuch as real-time whole body imaging for managed response and traumatreatment.

The stack 570 of this embodiment is somewhat similar to that describedhereinbefore (FIG. 24) with respect to the ultra-large flat paneldisplay embodiment. The first, second, fourth and fifth arrays 571a,571b, 571c, 571d are diffractive lenslet arrays which function askinematic lenslets and low f-number diffractive encoders field lenses tocollect and bend light to the first stack refractive lenslet array 571efor focusing onto a CCD array detector assembly 572.

X-rays 574 input from a source, such as from medical equipment, passthrough a phosphor screen 575 to the first element 573a in the stack(right to left). The right surface of this element 573a is a diffractivearray 571a, while the left surface is planar. The function of the firstelement 573a is to collect photons and collimate the X-ray input.

The collimated rays then pass through to the second element 573b in thestack. The right surface of this element 573b is a diffractive lensletarray 571b, while the left surface is a refractive lenslet array 571f.The bent rays emanating from this second element 573b are then directedtoward the third element 573c in the stack. This element 573c has afanout grating and includes a diffractive array 571c. Finally, thecollimated rays 575 leaving the third element 573c pass through to thefourth element 573d, which is a refractive/diffractive lens array 571d.The rays are then directed to a CCD 572. In one embodiment, each CCDarray camera 572 in image space has square pixels at a pitch of 25 μm,in at least a 512×512 array measuring 12.7 mm square. Thus, a desirableinput clear aperture size of the first stack is also at least 12.7×12.7mm square.

FIG. 27 illustrates the further and related embodiment where a plurality(in this case four) stacks are tiled together to receive the X-ray input586 from a large phosphor screen 587. Also shown are four CCDs 582, andassociated electronics that process the electronic signal output, all atthe control of an attached computer 604 connected to the PCI bus 600.The electronics include dedicated control boards 584 (controlled by acommon external clock 606 and power 608) for each CCD (i.e., a"camera"), along with a frame buffer 588 to capture the data from thecontrol boards 584, an accelerated co-processor 590 to process the videodata, and an enhanced display board 592. A hard disk drive 594 may beutilized to store data ultimately displayed on a video display 602.

Several CCD detectors with megapixel spatial resolution are commerciallyavailable from, e.g., Kodak, Loral Fairchild, Dalsa, Sony, Thomson CSF,EG&G, and Philips. CCD array cameras are also commercially available.Cameras appropriate for this embodiment range in size from 1K by 1K to2K by 2K nominal pixel resolution. One embodiment, for example, utilizesa 4K by 4K pixel resolution tiled array imaging system. This could beaccomplished, for example, with four 2K by 2K cameras for a two by twomatrix array of stack optics and CCD detectors, or sixteen 1K by 1Kcameras for a four by four matrix of stack optics and CCD detectors.

The imaging performance of the CCD detectors most likely limits theresolution and performance of a high spatial resolution, array imagingsystem rather than the stack optics. Although the stack optics willsupport any CCD pixel size, the demagnification and size of the stackoptics should be specific to the CCD chosen. In order for the stackoptics to effect the desired integration of the object onto a pluralityof detectors without loss of spatial information, the demagnified imagesof the object should just fill or slightly underfill the CCD activearea. If the CCD active area is overfilled by the image from the stackoptics, then a final integrated image with poor image interlacing of theobject can result. If the demagnified image from the stack opticssignificantly underfills its corresponding CCD active area, thenprovision must be made in software to eliminate the imageless perimeterof the CCD active area and appropriately match magnifications ofadjacent stack- coupled CCD modules in order to produce a non-distortedimage.

Standard mega-pixel CCD camera driver, logic and signal processingelectronics typically support only a few frames per second readout for a1K by 1K format or 1K by 2K format due to clock speed, timing and RAMmemory capabilities. Larger format CCD cameras use readout circuitrythat handles multiple 1K by 2K or 1K by 1K outputs in parallel. Clockrates are typically 20 Mhz and readout times of 50 ms or more combinedwith integration times of 50 ms or more provide less than the desired 30interlaced frame rate objectives.

High speed, DSP-based commercial frame grabbers with extended displayboards for video frame rate image representation on PCI or VME buscomputers are available. A dedicated Silicon Graphics computer, or 130Mhz Pentium processor with high resolution 2K by 2K monitor may beutilized. Frame grabber boards which can support up to 2K by 2K CCDcameras are also available. Systems integration combines the multipleframe grabber boards and adaptive software to integrate discrete cameramodule images into memory for display. The display is limited to asubset of the tiled imaging system image, but pan and scroll controlallow positioning of the target section of image space at any place inthe image file, including at the intersection among two or morestack-coupled CCD detector modules.

In addition to the above embodiments, the invention contemplates usageof the stacked array imaging system in numerous and varied applicationsbesides those described and illustrated herein. The details of theseother applications should be apparent to one of ordinary skill in theart in light of the teachings herein. The applications include: largearray imaging systems for heads-up displays; low light level imageintensifiers; large area, high resolution display systems; solid-statemedical imaging systems for high resolution whole body or thorax cavityin real time; low weight, flat panel cockpit displays or imaging systemsfor avionics or critical missions; spectral applications from deep UV tofar infrared; high performance infrared imaging systems; displays forenvironmental extremes; ultra-large, high resolution, flat panelelectronic wall displays; optical encryption systems for security; andother non-destructive imaging besides X-ray.

Many other applications for displays and imaging systems are alsopossible, including active systems where the field stop array at theintermediate image plane is replaced by a spatial light modulator, aphase conjugate medium, or other active or non-linear optical materialwith index matching properties (e.g., a quantum dot array) forwavelength selective applications. The spatial light modulator may beutilized in an application such as a compact optical correlator. Also,for a compact, low light level aid to the visually-impaired, amicrochannel plate having a flat glass phosphor screen input and a flatglass phosphor output may be employed.

Further, all of the foregoing has described optics that are totallytransmissive. However, a reflective optical device, such as a mirror,may be located at, e.g., an intermediate image plane when it is desiredto fold an image of the object back onto itself. In such an application,it may be necessary to utilize a beam splitter in front of the mirror.

Appendix A contains, for disclosure purposes, experimental data andresults conducted with respect to the teachings of the invention.Appendix B contains another exemplary application of the teachings ofthe invention including a design for a "chip on the tip" endoscopesystem. Appendix C contains another exemplary application of theteachings of the invention including a design to transform a 512×512 FPDto a 50 mm by 50 mm format. Appendix D contains a listing of otherapplications, features and benefits of the invention. Appendix Econtains another exemplary application of the teachings of the inventionincluding a design for a large area flat panel x-ray imaging system.Appendix F contains another exemplary application of the teachings ofthe invention including a design for a magnification and demagnificationsuch as for an x-ray imaging module, a compact optical correlator, and aflat panel display tile. Appendix G contains another exemplaryapplication of the teachings of the invention including a design for adiscrete pixel array magnifier.

Those skilled in the art should appreciate that changes can be madewithin the description above without departing from the scope of theinvention. For example, different lenslet array configurations,materials, and applications are easily made and envisioned.

The invention thus attains the objects set forth above, among thoseapparent from preceding description. Since certain changes may be madein the above apparatus and methods without departing from the scope ofthe invention, it is intended that all matter contained in the abovedescription or shown in the accompanying drawing be interpreted asillustrative and not in a limiting sense.

It is also to be understood that the following claims are to cover allgeneric and specific features of the invention described herein, and allstatements of the scope of the invention which, as a matter of language,might be said to fall there between.

Having described the invention, what is claimed as new and secured byLetters Patent is:
 1. In a method of manufacturing a microlenslet arrayof the type having a plurality of lenslets formed within a opticalsubstrate having a first planar surface, a second planar surface, and anormal vector that is substantially perpendicular to each surface, theimprovement comprising the steps of forming a first lenslet array withinthe first surface, forming a second lenslet array within the secondsurface, forming a plurality of lenslet channels between the lensletarrays wherein each channel includes one lenslet from each of thearrays, the lenslet channels between at least two adjacent arrays havinga channel axis vector relative to the normal vector such that the crossproduct between the channel axis vector and the optical axis vector isgreater for lenslet channels further away from a line extending along acenter of the substrate and parallel to the normal vector.
 2. In amethod according to claim 1, a further improvement wherein the step offorming a plurality of lenslet comprises the step of forming lensletsselected from the group of diffractive lenslets, holographic lenslets,phase modulating lenslets, index modulating lenslets, and refractivelenslets.
 3. A method of manufacturing a microlens stack having anoptical magnification for producing an image of an object along anoptical axis, comprising the steps of: combining at least two refractivelenslet arrays with at least one diffractive lenslet array to form alenslet array stack with a plurality of lenslet channels, each of thechannels having a sloped axis between at least two of the arrays, andarranging the channels such that the cross product between the slopedaxis and the optical axis is greater for lenslet channels further fromthe optical axis as compared to lenslet channels closer to the opticalaxis, thereby achieving the magnification selectively.
 4. A methodaccording to claim 3, further comprising the step of arranging thechannels such that at least two channels contribute to the image of eachpoint of the object.
 5. A method according to claim 3, furthercomprising the step of arranging at least one array so as to produce anintermediate image of the object and between other arrays, and furthercomprising a field stop located at the intermediate image so as toreduce the field of view of at least one channel.
 6. A method ofmanufacturing a scaleable large screen display from an electronicdisplay of the type having a center and a substantially planar surfacewith a surface normal perpendicular to the surface, the display of thetype selected from the group consisting essentially of an LCD display, acathode ray tube, and one or more laser diodes, comprising:selecting adesired magnification of the display; forming a tiled array of stackedlenslet arrays, the tiled array corresponding to magnification of thedisplay, the stacked arrays within each tiled array operating in concertwith every other stacked array within the tiled array so as to operatesubstantially as a single lenslet array, each stacked lenslet arraybeing formed through the following steps:forming at least one array ofrefractive lenslets into a first optical substrate and at least oneother array of non-refractive lenslets into a second optical substrate,the non-refractive lenslets being selected from the group consistingessentially of diffractive lenslets, holographic lenslets, phasemodulating lenslets, and index modulating lenslets, arranging the arraysinto a stack having a plurality of lenslet channels, each of thechannels having at least one refractive lenslet and one non-refractivelenslet, and wherein the step of arranging the arrays includes the stepof creating a sloped channel axis between at least two arrays andrelative to the surface normal, arranging the tiled arrays to operate inconcert such that the sloped channel axis is larger for channels furtherfrom the center as compared to channels closer to the center wherein thedesired magnification of the display is achieved.
 7. A method ofmanufacturing a stack of lenslet arrays for imaging an object to animage, comprising the steps of: forming one or more non-refractivelenslet arrays and one or more refractive lenslet arrays, forming aplurality of lenslet channels and arranging the channels such that eachlenslet channel has at least one refractive lenslet and at least onenon-refractive lenslet, and arranging the lenslets within a channel toachieve a selected magnification between the object and image.
 8. Amethod according to claim 7, further comprising the step of forming atleast one of the arrays through one of (a) molding of an optical gradepolymer and (b) coextrusion of an optical polymer, with an opaquepolymer.
 9. A method according to claim 7, further comprising the stepof fabricating the lenslets from a negative relief to generate surfacefeatures, plus fiducial marks and mechanical assembly features, thenegative relief being fabricated into a metal, ceramic or hightemperature composite master.
 10. A method according to claim 9, furthercomprising the step of transferring a positive master in glass,semiconductor or crystal material to a ceramic or elastomer template toform a negative mold master.
 11. A method according to claim 7, furthercomprising the step of forming the arrays from different opticalmaterials so as to correct for optical color aberrations.
 12. A methodaccording to claim 7, further comprising the step of manufactured atleast two of the arrays through replication, including the steps offabricating a mold from a negative relief of the refractive andnon-refractive lenslets, and of fabricating fiducial and mechanicalassembly features within the stack.
 13. A method according to claim 12,further comprising the step of fabricating the relief from a metal,ceramic or high temperature composite master which is produced bymicromachining or by direct forming into a master mold material.
 14. Amethod according to claim 13, further comprising the steps of coatingthe master with a release agent followed by one of (a) an epoxy, (b) apolymer, (c) an optical quality organic, and (d) a sol gel material toproduce a thin sheet of material with lenslet array features, fiducialmarks, and mechanical assembly features.
 15. A method according to claim7, further comprising the step of fabricating opaque interstitial areasto provide for stops and to eliminate or reduce optical crosstalk amongnearby lenslet channels.
 16. A method according to claim 7, furthercomprising the step of fabricating the lenslet arrays with fiducialfeatures to facilitate alignment and registration of lenslet arraychannels in Cartesian x-y and rotational coordinates.
 17. A methodaccording to claim 16, further comprising the step of locating thefiducial features at one or more of (a) outside of the lenslet clearaperture and (b) interstial to the lenslet array features.
 18. A methodaccording to claim 16, further comprising the step of arranging thefiducial features as one or more of (a) a frame around the lenslet arraymask, or parts of the lenslet array mask, (b) within interstitialregions to the lenslet array channels, (c) horizontal or vertical lines,sequences of lines, crossed lines, circles, squares, hexagons, othergeometrics or combinations of geometric shapes.
 19. A method accordingto claim 16, further comprising the step of arranging fiducial markssuch that a Moire pattern is generated upon assembly of the arrays,thereby indicating proper registration.
 20. A method according to claim16, further comprising the step of making the fiducial marks andassembly features out of material used in the masking of theinterstitial and surrounding regions of the lenslets.
 21. A methodaccording to claim 16, further comprising the step of making thefiducial marks and assembly features as etched features within the arraysubstrate.
 22. A method according to claim 16, further comprising thestep of making the fiducial marks and assembly features out ofmechanical spacers for placement within the stack.
 23. A methodaccording to claim 16, further comprising the step of forming thefiducial marks out of one of a material that transforms from a solid toa liquid when subjected to heat or other activation such that a surfacetension is created to promote alignment of the stack.
 24. A methodaccording to claim 23, further comprising the step of retransforming thematerial of the fiducial and assembly features back to a solid, therebybonding the stack together into a monolithic structure.
 25. A methodaccording to claim 23, further comprising the step of assembling thestack with the material at one or more of (a) edges of the stack or (b)internal locations of the stack.
 26. A method according to claim 16,further comprising the step of immersing the arrays with adhesive formonolithic bonding of the stack.
 27. A method according to claim 16,further comprising the step of adding thru-holes within the stack so asto provide for the insertion of micromechanical pins which assist stackassembly and which mechanically tie the stack into a monolithicstructure.